I do not ride competitively, but plan on doing some longer distance rides (+30 miles). I've read that better components are lighter, run more smoothly, and last longer. Out of those three categories, durability (lasting longer) is the only one that really matters for me, as long as the components don't break all the time and get the job done. Are the main advantages of high end components the reduced weight and smoother operation, or are they significantly more durable as well?
I assume that you're talking about road biking. I can give you my opinion after using these groups for a while: Shimano Sora, Shimano Tiagra, Shimano 105, and now a full Shimano Ultegra.
All work, when properly adjusted and when shifting correctly. You have to do your homework and know how to shift smoothly, and adjust the gears. Whoever tells you that something is "not good" or "does not work" is lying or wants you to expend money. But of course different levels are there for a reason:
Weight: More expensive is lighter. Stiffness: More expensive is stiffer, therefore transmitting your power better without loss of energy. Ergonomics: More expensive groups tend to have a refined shape. Reliability: More expensive groups tend to stay tuned longer than less expensive ones. Shifting under pressure or more than one gear at the time: Expensive groups allow you to do it, cheaper ones don't. Smoothness and speed: Shifting is faster and smoother on expensive groups.
If you notice, I put smoothness and speed last. It is usually one of the reasons that people mention as being key, but in my experience proper adjustment and proper shifting technique are more important than the group. My bike with Sora/Tiagra shifts as smoothly as the Ultegra after adjustment. But the other reasons are important to many people. Even if they don't compete they may want a light, stiff, and reliable group that makes the experience of biking more pleasurable (although the real pleasure is riding, of course), and they are willing to pay for it. They are undoubtedly "nicer".
Regarding durability, I'm skeptical about people's comments. Most of the times people change chains and cassettes because they are worn out, and upgrades/changes the rest of the group's components as new models appear, not necessarily because they don't "last". If you're a recreational rider, whatever you buy will "last" more than you will need. I've seen 20 yr-old bikes that work perfectly, provided that the user changed the chain and cassette regularly. But remember durability and reliability are two different things.
At which point is not worth expending more money? Difficult to tell, but here is my suggestion (take it as a suggestion and nothing more):
Dura Ace or Sram Red if you compete. Ultegra or Sram Force if you are an enthusiast that races or values to have a performance group. 105 or Sram Rival if you want a very nice recreational group. Tiagra or Sram Apex if you want a solid recreational group. Sora and below if you are a recreational rider that does not want to spend too much money.
Here's a little bit of information that's in contradiction to "higher end equals better" Lower end components can sometimes last longer and be less problematic than the higher end components. In order to shave off every single gram they sometimes have to skimp on materials. Also, the tolerances are much tighter, and high end components can often be difficult to tune because fractions of a millimeter matter. An 8 speed derailleur can be quite a bit out of tune before you'd notice. The same can't be said for a 10 speed. With so many gears, there's very little room for error. 10 speed chains are thinner, and therefore stretch and break more.
Don't go for very low end stuff, because it often will be made bad, and will break faster. But different components are built with different goals in mind. Very high end parts are often built for racers, who have professional mechanics who can ensure that everything is tuned properly, and parts are replaced more frequently. If you buy decent components and maintain them well, you'll get plenty of life out of them, and you'll be able to replace them when it's necessary, instead of waiting until it's too late.
This very much depends on how exactly you define the classes of components and what type of riding you plan on doing. The definitions are not standardized, but component ranges from each manufacturer are easily ranked. The following are the MSRP of complete group sets for Shimano (the price ranges are similar for other manufacturers).
If you truly only care about durability and don't care about either weight or smoothness of operation, then you will probably find that mid-range components are a better value for you than high-end components. Even if high-end components (e.g., Dura Ace) turn out to be more durable than mid-range components (e.g., Ultegra, 105, maybe Tiagra), this would probably not justify the more-than-double cost if the only thing you care about is durability. If you had to replace every part, you would still come out ahead in terms of dollars spent.
Mid-range components (e.g., 105, Tiagra) are far more durable than low-end components (e.g., Sora, non-series). Any but the most undedicated rider can appreciate the benefits of mid-range over low-end components. I personally bought a used bike with Ultegra that cost about the same as a new bike with Sora, and I feel like I would be wasting my money to get a bike with Sora.
From how you describe your riding, it sounds like you would probably find the best value from mid-low to mid-range components, but this completely depends on the degree to which you are constrained by cost. Because more expensive components can sometimes be less durable than cheaper components, it is too easy to be dismissive and assume that the high-end components are Veblen goods (see The Online Photographer for a discussion related to photography equipment, a similar market).
One person can't say whether a product's price is "worth it" to someone with a completely different income and lifestyle. I once talked to someone who owned "Lance Armstrong's bike" (after I asked, it turns out it was the same model, not a collector's item), which was an example of the 'high status of allegedly "pro" products among amateurs'. But this person was happy with his bike and seemed to be at least somewhat appreciative of its benefits over a low-end bicycle. Few cycling products qualify as Veblen goods:
In the end, each person must decide what they need and are willing to pay and whether a product provides benefits that they will appreciate. Don't jump to the assumption that other non-competitive riders are wasting their money on expensive crap, but also don't feel guilty if you don't notice or appreciate the difference in weight between two bikes. And if you end up doing longer or steeper rides, you can always change your mind later.
If on a road bike anything that is Sora / 105 level will work wonders. Deore or similar will work fine.
What is more important that the group-set IMO is the general quality of the cranks and chain-rings. The better the forging the longer they last.
TBH I don't think it really matters once you get to decently specced bike these days because modern chains and chain sets are so good that they run years with few problems. I have a Sora kit that has almost zero maintenance for several years and the large chain ring is starting to want replacement just now.
Also It matters how it feels a lot as well. Crappy pedals and cranks will make it feel like you power transfer isn't brilliant; even the pressure in the tyres affects how I feel when I ride.
I think tbh there is a lot of focus put on one part of the bike, yes crappy shifting can ruin riding but also having a crap set of cranks or wheels also hurts just as much.