I guess you could call this is a "confession" post, but I can definitely speak for the benefits of bringing an interesting old car over one that's new and has actual racing provenance.
When I emailed Judge Phil to ask what starting value to use for my slant six-powered, automatic, 1964 Dodge Dart that I'd owned for 10 years, which ran when parked and basically just needed a carb rebuild and new valve stem seals, he told me $2.25, or "one penny for every CID." We spent most of our budget money on shock absorbers and new leaf springs.
After our first race, which was remarkably trouble-free except for ludicrous oversteer caused by stiff new rear springs and squishy old front torsion bars, he gave me a residual value of one penny for every lap we turned (something like $1.60). We responded by replacing our leaky radiator with a used one from an unidentified Toyota truck. And also by putting $600 worth of aftermarket suspension parts under the front end.
At our second race we still got Class C, zero penalty laps. I didn't even bother to ask for a residual value since nothing major needed to be done, but I expect it would've still been in the single digits.
Of course, Phil wasn't giving us much of an unfair advantage with all the budget leeway; the car was still slow as hell. (It turns out the judges mostly know what they're doing). But it's been really nice not having to worry about keeping track of nickels and dimes. If something like a water pump or alternator is doubtful, we can just replace it without worrying about getting sweated at the next race.
Command Pilot/Flight Director, Escape Velocity Racing
Index of Effluency, Heroic Fix, Class C Trophy, now hopelessly gunning for Class B.
Currently 1-2 vs. Team Fairlylame in the Class of 1964 Championships