1966 Valiant...should I part or fix it?

If you have more than one project going now, and your resources are limited, I would suggest you consolidate down to one car. Focus on one car at a time.

Reality check: the Valiant sounds like like a base model stripper rustbucket with a few nice parts bolted on. This is a case where the whole is worth less than the sum of it's parts. The parts you listed, grilles, fenders, brakes, seats, wheels, together might get you $1000 or so. How much would that help your 72?