A watch enthusiast is someone who
1. reads a whole lot about watches and wants to broaden their knowledge about em and what makes them tick
2. spends too much time on too many different watch forums (lurking / learning or contributing when they feel they have something of value to share and is of benefit to that community)
3. is someone who does a lot of research into watches they want to buy but may fall in love with a watch (with very little research done on it) and just buy that... and then buy the watches that they have been researching on at some other time too 
4. would spend a significant part of his bonus on watches=> money coming in feeds the addiction
...
i think i can go on but won't right now as its getting scary
... to sum it up, its all about passion and love really.
a collector collects but may not have that, they may be driven by other motivations. an enthusiast has it in spades...
have a good weekend all
cheers
raph