I can definitely relate to this. I've gone through my collection several times wondering what I'm okay with parting with. I recently went through all of the posters I had stored (I had all my posters stored in four large frames) and I took out 80 some posters I didn't want anymore. I've sold quite a few already and the best part for me is that a lot of those were ones I got cheap or free so a very high profit margin. I end up using nearly all 50 free listings on eBay each month (though some of those are relistings of stuff that didn't sell before) and I've gotten a decent amount back that's gone straight to my current preorders.
Feels nice man.