Like most people, I chose to modify my car to please one person, the owner, maybe that sounds selfish. But one thing I've discovered (after owning over 100 cars) is that the cars I personalize tend to be the cars that I want to keep a lot longer than the cars that I leave perfectly stock.
I never make a modification that can't be undone in hours, and returned to stock. But the enjoyment factor out weighs any monetary loss or gain I may or may not see, by making my car look exactly the way I want it to. Thus, it's priceless to me.
I will agree, that most untouched "original" classics do bring more $$$'s at collector auctions, and are easier to sell. But there are always exceptions to that rule, what with the crazy prices that some "restomods" are commanding these days. All it takes is finding that one buyer who's willing to pay a premium for your idea.