1. I like archiving/organizing stuff been that way since I was a wee one collecting pokemon cards. I pretty meticulously track my collection on RFgeneration and I have 935 submissions there currently most of which are game/variant additions since I haven't gone on a solid scan/screenshot binge in a long time
2. It gets me out of the house. I'm kind of a hermit and a loner so I rarely get out much aside from work. About my only regular activity every week is going out to the pawns/flea market to find some new stuff.
3. I enjoy reselling but I also hate selling things that I don't have copies of
4. Ego plays a part in pretty much any massive collection and I just really enjoy the idea of having a massive private library that I have access to any time I feel like it. I also like slowly climbing the collection list over at RFgen
As for actually playing them I am constantly playing. Sure it's mostly new gen stuff since I'm more of a story driven player, but I do dabble about in my retro stuff pretty frequently. I most likely will not play everything I own within my lifetime, but that doesn't bother me.
I also think it will be pretty interesting to figure where my collection goes after my death. I would either like to donate it to a museum or library system, but in the case that it all ends up in a estate sale that would be cool as well. Honestly I'm looking forward to estate sales in the next decade or two starting to crop up with more interesting electronics and etc. that have been stowed away in attics and closets for years.

