Depends on what you're looking to sell. People will pay up for "out-of-production" kits that you can't get anywhere else (think Johan). Kits that are currently on the shelf in your LHS aren't worth the extra shipping to most. Just remember that eBay takes a 10% cut on the total sale (including shipping).
I like to have 3 going, in various stages so there's always something to work on. I try to get a little something done every night in front of the tube, but sometimes all I do is stare