I've been doing restorations for 22 years and the one tool category I see people underinvest in is measuring equipment. Tape measures and eyeballs aren't sufficient for body alignment. A good trammel gauge kit for checking diagonal measurements, a digital angle gauge for suspension settings, a proper feeler gauge set for carb adjustments — these aren't glamorous but they're how you get things right.

The second category: lighting. You cannot do bodywork in a dim shop. Every shadow hides a wave or a low spot. A good inspection light on an extension is as important as the sanding block itself.

Spend the money where it affects quality. Nobody sees your fancy tool chest. They see the panel gaps.