Pervert (positive)
When talking of someone who is really into a thing, especially aspects of it that are often thought to be off-putting such as jank in old video games or the hassle of maintaining a trash-picked bicycle, a term I've been using more and more recently is "pervert" or, if in company who are not familiar with the usage, "pervert (positive)".
I am not entirely sure where I picked it up. I would want to say I remember Kayin using it, but I'm not entirely sure. I did pick it up within the last couple years, so Cohost is a pretty reasonable guess for where I picked it up from.
I'm interested in hearing about others' usage of the term with same or similar meaning, so send me an e-mail (see my home page for my address) if you've encountered it.