Honestly, just play until you are done imo. Nostalgia is different to everyone, but undoubtedly one of the strongest forms of irrational love there is. Here's the thing though: If you truly love something, the nostalgia or appeal of that thing doesn't wear off. If you think the nostalgia will wear off, then that might be for the best. Every time I dive back into my Rock Raiders lego, I feel a strong sense of nostalgia, but also a genuine love for it. However when I play the Rock Raiders game, I feel the game design frustrations so often, I question if it's worth playing the game. It's still enjoyable, but it's impossible to say it's perfect. But the feeling... the music, the sounds, the charm, that is where the true nostalgia lies, and I still don't get tired of the soundtrack to this day. I think a lot of people feel the same about Lego Island: The power is in the charm of the characters, not the graphics nor the controls, but to someone who hasn't played the game before, it's probably really boring and impossible to get into.
Or think of it this way: If you bottle up nostalgia in order to use it later, or to never spoil it, then what's the point of nostalgia? There is probably hundreds of things you liked as a kid that you know you don't like anymore, be it crappy browser games or TV shows made specifically for kids. The nostalgic love for those doesn't wear off because you indulged in it, it wears off because it truly wasn't that good or you don't enjoy it anymore. There's so much stuff I had as a kid that just doesn't interest me in the same way anymore. I still feel nostalgic about it, but not enough to feel that it's some perfect time capsule never to be broken.
Realising the things you are nostalgic about aren't perfect is a healthy process of maturing, in my experience, and has in my case actually helped me enjoy nostalgic content more. It's all up to you if you want to uninstall the game of course, but the real question is why deny yourself the experience?