Modify or buy another car?

[Mayhim]

You mod a car until you can't find anything else or don't feel like fooling with it for a while or forever.

You stop fixing a car when you reach the end of your tools (and can't/won't buy more), reach the end of your ability (and don't want/can't learn or figure it out), or get tired of fooling with it for a while or forever.

You buy another car when you get the itch bad enough.

At least, that's what I do...your mileage may vary.