This sounds awfully naieve of me, but doesn't every kid obsess over the things they enjoy - I thought it was the way the young brain works. I'm not downplaying stuff here, its just everyone I know has or had obsessions as a child, and truth be told, I cannot see much difference between the descriptions given here, my own experiences, and those I have seen of the people around me.
From 1992 (I was 5) till when ever Space Precint stopped showing on BBC2 around 1996(well whenever they stopped showing any Gerry Anderson material) I had an obsession with Gerry Anderson products, for those unitiated, that is Thunderbirds, Joe90, Captain Scarlet, UFO, Space 1999 and Space Precinct.
I know he did others, but they weren't shown on the Beeb so I never got to watch them.
I had alot of the Thunderbird toys, my mum even tried to make me a very big TB2.
I get this kind of branched into scifi as a whole, with things like Space Above and Beyond.
Ultimately though, it led onto my Star Wars addiction, which has slightly waned recently as I realised I cannot go and spend all of my money on action figures, but I still get great enjoyment looking in the window of the local collector shops and have my computer guarded by Boussh and Bossk!