All of that should be predicated on the answer to the question "How much of the outcome of this work do I truly have influence over?" and if the answer is none, and those extra hours making sure your code is really nice, should only be spent within the constraints you're being paid for. Are your requirements fulfilled, but you were pretty fast and have a bit of extra time to clean things up? Great, that's fine. If you spent your 8 hrs that day, the requirements are complete and there's no more time you're getting paid for, and you don't get to determine what the positive outcome for you is if you donated your weekend to fixing something management doesn't care about and won't pay you for, then don't, and stop having pride in it.

You own it if you own it, keep your personal investment at arms length, lest you become a Jason Bateman character desperately putting in those extra hours so one day hopefully you'll be blessed with that VP position or w/e.

That said, of course if you've achieved something within a fairly tight constraint, ideally you're compensated or recognized somehow for it. Extra worthwhile hours should also be compensated for obviously. But if nobody is willing to pay you for it, it's probably your own undoing.