A car that big can be reasonably fast, but you'll still see a lot of tail lights. Speed is horsepower to weight. Now that said, that is a nice car and would be an ideal 'cruiser'. Speed is only one factor to the car hobby. Style is another. That's one thing cars of the last 30 years or so are lacking.

I'd leave the internals of your 352 alone, maybe add an intake, carb, possibly a cam and headers. Toss in a exhaust system with some 'mellow' sounding mufflers and enjoy the car for what is appears to be; a nicely preserved 40 year old car. I'd bet that even with the mods, you'd still keep the cars resale because you haven't made any changes that can't be changed back. And keep the original parts for the next owner in case he wants them.

By the way, if it's me, I'd also get a set of period style wheels like Cragar S/S or American Racing Torque Thrust D's. Yeah, a lot of cars have them, but for a 1965 car, they still look great.