wasn't really into the 63 Valiant when I bought it 4 years ago, but it was a clean inexpensive A body that I now drive daily. the looks have grown on me. Mechanically it is all original- wish I had better brakes though.
I really don't think that a brake upgrade would hurt its value, unless you want a trailer queen concourse car. I have late Mopar brakes on my 64ragtop, and modern disks on the AZDart. That car was NO fun with the original 9" drums in modern traffic! MUCH better now!
I loved the '63 darts when they came out, drew pictures of 'em in high school art class! Now I own a '63 and 2 '64s. Plans are for a pretty warm /6 for the '63 and fairly hot small blocks for the others. My sig pretty well says it all!