Well, I'm counting whatever I buy, toy-wise. I just snagged an Acklay the other day. I don't need it, I already have one, but it is for trading, so I laid out cash to get something for trade bait, therefore it is going to toys.
Same with McFarlane sportspick variants. I'm not keeping any of the Gaborik variants I'm getting but I am trading them to get stuff I want, so they count. After all, I paid to get them. I'm not necessarily keeping many of them at all, but all are being used to trade for stuff I want so I think their value should count.
As far as Ebay stuff goes, that's up to you. I'm just trying to keep track of every dollar I spend on toys/collectibles so I have an idea what I spend. Anything I earn from sales on ebay goes (predominantly) into my paypal account that gets turned around on toys anyway. So even if I buy something at retail, triple its value, I'm likely to spend that money on my collection. I don't think it's fair to credit my 'tab' without taking into account the cost of getting that item in the first place. Theoretically you could take that profit margin and pay down your mortgage sooner. Theoretically. If you do that, feel free to credit your account. I know I won't.
Just toys, busts, props, replicas. comics, DVDs, CDs, stereo equipment, etc don't count for this. By all means, be like Mikey
and keep track if you want to see what you spend on 'disposable' items, but I didn't intend for that here.
I'm not expecting any declarations of income, profit or otherwise. What you spend is what you spend. Where the money comes from is your business. If you know a great way to turn small dollars into big dollars on ebay, go for it. If you rob a bank, hey, that's up to you, but I expect when/if they catch you, your toys won't be going to the hoosegow with you