I mashed my 8 speed Shimano Acera rear derailleur in a crash over the weekend and need to get it replaced. Is it worth spending a little extra money and installing a slightly higher-end derailleur, such as a Shimano Deore or Alivio derailleur, or does it not really make all that much difference without replacing the whole drivetrain? (Which I am not willing to do) The bike is relatively new so the other componentry is in good condition if this is a consideration. Thanks
Any 8 speed derailleur should work fine - the higher the "grade" the better made they are.
However the incremental difference is slight, and simply "not mashed" could be all you need as long as it performed satisfactorilly beforehand.
Another way to view it is that the same part has a cost of $x, and a fancier unit has cost $y, but you have to pay $x so the cost to upgrade is $(y-x)
Do check the specs first though - if you can count the teeth on both the biggest and smallest cog, then look up the specs of the part you want to buy and make sure it suits. No point getting a fancy derailleur that won't handle your current cassette.
Also consider whether your chain was damaged in the crash, and whether a new one is appropriate. Might be better to do that than spend more on another mech, which could go the same way as the first one if you crash out again.