This is always a tough question that everyone has to answer from time to time, and isn't really specifically related to an RV either.
The question I always ask someone when they ask me this question for a car or truck is if you just went and fixed what you thought may be wrong, how much of a new vehicle would you get for that same money? The answer to that is likely something that is junk and clearly a camper v's a car has a lot more systems in it that could also face the same question sooner or later. The big unknown is if you spend money to fix one item, you will never know what or when the next item that needs to be dealt with will show up.
If reliability hasn't been an issue in the past, then it's probable that it will still be reliable even after various systems would be replaced. If it's been problematic, then maybe that's the deciding factor leaning more towards replacement. If all the systems inside are operating well, that also says something for fixing what needs to be fixed. For fixing things, you can either do it sooner or later, depending on what may happen and where you're at, which nobody ever knows. One breakdown on the road could be fairly expensive and ruin previous plans.
This probably didn't help you, but there is literally nobody on this forum who can give you a specific answer because it's so subjective to your specific conditions and situation.
Personally, I've always defaulted to fixing what I have if it's reliable, I don't dislike the car, or want something different and something that seems like it's got a lot more life in it. But, that's me.