I sold my entire collection about 2-3 years ago. It started originally as just G.I. Joe. I had a lot of original RAH carded figures, eventually got the JvC stuff, through Spytroops, all the way to 25th Anniversary.
Along the way I discovered Hot Toys AVP Predators and ALIENS Colonial Marines and before you knew it. I had LOTS of Hot Toys. So I started right when Hot Toys "blew up" in the West. I had every ALIENS Colonial Marine, the original Hot Toys Superman that wow'ed everyone, and soon they were joined by Iron Man, Wolverine, other Aliens and Predators, Sideshow statues, movie figures, etc.
Not only that, I also had MULTIPLES of the figures I really liked and kept those stored away.
Eventually, I was getting ready to move and just realized I could let it all go and feel alright about it. At that point, the money was a bigger concern to me and I sold it all. The GI Joe collection, the Hot Toys, the Sideshow, Medicom, etc. I used most of the money to pay off my car and it felt really good to do so.
I didn't feel any need to be a completist, but I felt that I just didn't need or want them anymore. I still appreciate and respect the hobby and ironically, a lot of my favorite figures have already been redone in better versions (ie: the "classic" Predator and movie Spider-man) so I have picked up some figures here and there but nowhere near to the amount that I had before and I probably won't go back to that ever.
If you're thinking about letting go...do it, it's not the end of the world. Use the money to pay off any debts, travel, on a new hobby, etc. Keep your favorite pieces and sell the rest, hopefully to someone who will appreciate them just as much as you did.