Paint for my '75 Hang 10?

Here's my opinion for what its worth, which isn't much...

Like you said its rare but in not worth anything to speak of really... If your not doing a Barrett Jackson restore to squeeze every bit of that $10K out of her then paint the car the way you want it. You'll have the only Blue or whatever hang ten... Do something fun to play off the original pin striping and make it yours. Its always going to be a Hang Ten... Let the next owner worry about making it 100% original... they might get $12K for it then.. j/k

Its not a Hemi car so does it really matter.....

I'm not familiar with your car, is it numbers matching? regardless I would make it yours. Also you have a good selection of colours to pull from in the interior so you can make it any colour and still have things match.

Its only paint.