Does planning every detail ruin the magic of a vacation?

No it is not

No, because unprepared is the worst.

Im the type of person who like to just relax. I would rather sit in the pool than run around trying to see all the sights. The only plans I'm intrested in is finding a good beach and yummy restaurants.

I think maybe sometimes it does

It depends on the person. Some people prefer to know exactly what to do at what time and how much it will cost. Others are ok with going with the flow and finding things to do on the fly. I prefer planning, but doesn't have to be every detail. I'd be ok just with details on the flight/hotel, find food/activities as we explore.

Yes just let things happen