Agree Jo - the smell hooks me more than anything! Old Sci-Fi (Heinlein, Norton etc) just enthrall me - the cover art, the browning musty paper... LOVE it.
Used to collect military firearms and accoutrements. Down to a mere handful now, from 196 a few years back. Sold most, made close of $80K.
Also used to collect model aeroplanes (mostly) and some spacecraft models. When wife and I moved to Perth, sold those up, and got enough from the Buy Now on eBay to afford the trip over and rent for 2 years!! I had THOUSANDS of kits, ranging from ultra scarce (Frog, early Airfix, early Monogram and Revell etc) to VERY limited production.
The joys of once being a bachelor on a good wage
