I tend to live in the fix it camp, but it depends on the circumstances. If my 1980’s top of the line downtube shifters decide to hit the dust (as if) I’m not going to look for that NOS cherry or the newest equivalent because that’s not cost effective. On the other hand, since I have a good local bike coop (do you?), I know I can get a functional used pair from the parts bin for under $5.

The only time I’ll buy a new bike is when the cost of things I want to replace exceeds the price of a new one. When you’re doing your own labor that’s hard to do unless you have say an 80’s bike and want brifters and a threadless headset. Occasionally a screaming deal will come along to justify trading up, but not frequently unless you’re taking a large step/changing the type of bike.