Sorry to arrive late to the party. DATBRAD hit it right on the head as far as I'm concerned.
An altered copy of a recording can certainly have more clarity, more fullness, or more anything else (or conversely, less of whatever's bad) than the original recording. There's a whole profession of "sound restoration" and "mastering" that specializes in making this happen, and it can sometimes happen by accident as well. Naturally the better the recording you start with, the better the result will still sound.
The people who are really good at this have the best tools available, including their monitoring systems, and they do this every day of their working lives and have done so for decades. They've developed a way of listening to sound that is extremely acute. It's a specialty that takes much development and practice. Not every professional audio engineer is good at it.
Regrets can definitely set in later, though, just from the passage of time and the normal, continued growth in your perceptual abilities through experience. Usually the regret is, "I wish what I did back then wasn't so obvious now." You can always do more of something later, but you can't very well put things back the way they were and do it over from there, unless you have the straight, unaltered original on the shelf.
--best regards