That's why I said, "knowing when to sell." I should have added, "and where."
No, you almost certainly are going to lose money if you are pressured into selling a gun in a hurry. Your LGS and/or pawn shop are there to make money, and to avoid risk. They are typically going to give you about half of what they think the value is ... if they are even that generous. If you must sell, the online sales and auction places are the best, so long as you market the guns well. Most of my (very few) GB buys were good ones because the seller sucked at listing the things so that people would be able to find them.
My point is only that is there is no place you can sell an entire collection quickly and get a decent price, so even if you view a collection as an investment, it's not a liquid one at all. Sounds like you agree with that.