You do see a lot of people riding beaters with flat tires and I get the impression that they do not really like riding their bike but it's better than walking. Seasonal tuneups are pretty popular for people who actually like riding and do so recreationally. Working with the cables and derailleur can be vexing if you don't know what you are doing. It's also nice to support a local business that serves your hobbies, but that's just me. Trade the wd40 for some triflow though. wd40 does not stand up to water.

Bar tape, inner tubes, and lube are all I really buy regularly; and the tape is just because I am vain and like to change up the look.