Presently, I am riding a women's Trek road bike. I ride mostly flat roads and sidewalks, approximately 125 miles/week. My bike is 6 years old and I need a new bike. I felt this bike was too high maintenance for me as I averaged a flat at least once/month and often spent $300. at my yearly check-up, replacing the chain, cassette, etc.
If it’s just about maintenance costs: Maintenance of a new, regular bike is going to be just as expensive or even more expensive because newer components usually cost more (e.g. 11 speed components vs. 10 or 9 speed).
You could get a low-maintenance bike, for example the chain on a single speed or internal gear hub lasts much longer and there is no expensive cassette which needs replacement.
However, unless almost everything on your current bike needs replacement my advice would be to keep it, but:
- Get more puncture resistant tires to avoid flats. They’ll roll slightly worse or cost slightly more but with “puncture proof” tires you’ll basically never suffer a flat. Usually the rubber also lasts longer.
- Regularly check chain wear and replace the chain early enough. This will reduce wear of the (more expensive) cassette and chain rings. And of course keep the chain clean (I just wipe it down with a rug, others go as far as taking off the chain) and well lubricated.
- Get (relatively) cheap chains and cassettes. For example Shimano 105 chains and cassettes are much cheaper than their Ultegra or Dura Ace counterparts while performing almost identically.
- Do as much maintenance yourself as possible. With your weekly mileage it absolutely makes sense to get appropriate tools.