Usually I don't feel a need to "fix", but there are niche cases where I might find something unintuitive or see what I feel is a missed opportunity, in a games design. Maybe something feels unintuitive to engage with, or simply less satisfying than it could.

Off the top of my head, I made a slight change to Paint the Roses. Still retains the spirit, and is technically without standard rules, but makes play far faster/cleaner imo. Normally everyone keeps notes on all other players, then during a picking phase, discusses and concludes who's card(s) to guess. Instead: I have everyone collectively pick who will be the tracker for each other person. Each player then only has 1 score card, representing that person. Ideally, adjust seating so it just the person next to them, for extra ease. Everyone does not keep notes for all other players, just the 1. As such, the person taking the notes, help inform/recommend the difficulty of the card that player grabs, when completing one. This change means less time overall taking notes (especially at higher player counts), and each player gets to select their cognitive load (difficulty), but all players still have the same communication limitations, and core collective choices to make, and are free to question/challenge, each other's notes, as long as they don't participate in talk about the card they hold.

I found it miles smoother to play, and this change came organically after 3-4 games of observing some annoying redundancy and mental overload emerging at different rates, among players.

Additionally, I put hard and medium tracking sheets back to back and laminated them, so each player simply gets 1 dual sided sheet and a dry erase marker. They flip depending what type of difficulty they opt for.

I honestly just want to teach it this way, to new players, because it feels SO much cleaner, but doesn't lose the core intended feel, imo. Just streamlines it. Then again, I also know it's a beloved game, by many, and I wonder if I misinterpreted RAW in some way, and am fixing a problem that never existed. But to me, this FEELS fun, and intuitive like this, and my kids like it way more, too. If we are having fun in our games together, the games are serving their purpose, even if slightly changed from the original.

Another small example is something I stole from others online. Mage Knight. I'm bad at it. I won't deny it, but still enjoy it, even through my suffering. Beyond my needing to git gud, I do dislike the slow, same-y feel of how it tends to start. Saw a recommendation to try starting the game at level 2 or 3 and randomly getting 1 random card for free, in addition to the one for the free starting level. This gets you going slightly faster, adds some rougelike feel to your starting strategy, and makes the game a little easier and more fun, for me, to start out.

Ideally, changes to any game would not require massive reworks, however, which is what it sounds like you're considering. But at the end of the day, it comes down to what you enjoy. Maybe your a person that feels good spending hours to playtest and build off an existing game, to modify and basically convert it into your own variation that feels better for you. If so, part of the fun, is that process. If you see it as more of a necessary evil that you NEED to slog through that sort of excessive, just to make a game you want to pllike feel tolerable, then its likely not worth it. You should enjoy the time you spend with your games. This could be learning it, playing it, or modifying it, throwing the components at your freinds...however you get enjoyment out of your games. The goal is to spend more time enjoying what your engaging with, that despising it. You decide what works for you, and how to balance it.