The great thing about old movies is that they feel like a time machine. I generally avoid watching the ones I have really good childhood memories of as there is quite a high chance that gets ruined. However, I do like to rewacth movies that get really high ratings but where I was too young to fully grasp it (Like Mulholland Drive / Donnie Darko just to name a couple).
Also many old classic films that I have yet to watch including some westerns like the good the bad and the ugly. There is so much out there to watch but so little time.
Enjoy the rewatchs!
I sympathize with the lack of time. I'll have to check out Mulholland Drive. I have heard of it but never seen it. Good Will Hunting is another I've never seen.