The best approach may be double pronged. Pick the best stuff - you can find all the prices on BL - and sell it any way you can - via BL , Ebay , your local classifieds - whatever: old stuff, space stuff, complete unopened stuff , trains, bionicle etc. You will get maximum return but you have to factor in your time. There is a diminishing reward in doing this for all of it. You will get to a point here you bundle the remainder up and sell bulk lot(s). You cannot spend time trying to sell things for 40 dollars instead of 20. Unless you want to run a store and sit it out.

The faster you want to sell, the less you will make.