Getting back to the original question...
I buy and sell models from time to time. IG armies seem to cost the most because a) there are so many models and b) someone is always looking for them. With the new IA:13 and the Renegades list, there should actually be more people looking for them now than ever.
I suggest you start there and then make plans for what to do with the other armies.
From the way you describe your playstyle, you sound like someone who would appreciate a Grey Knights army. There are no subpar units there, and it's relatively cheap to get a GK army compared with others.
Good luck!
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