There are some valid points here. Assuming a gun is purchased at a reasonable price and sold in roughly comparable condition in a non fire sale 'got to sell it today' way they hold their value quite well. Do however note there are a few qualifiers there.
I think this decision is a lot easier for gun enthusiasts/ tacticly minded type folks than survivalists or their toned down better dressed cousins 'preppers'. A shooter can buy the cool new gun they want and assuming it's not a financially ruinous move (buying a SCAR-H on a credit card, etc) then rock on. A survivalist on the other hand has different stuff to look at. It's not just 'do I need this gun' or even 'do I want this gun' anymore.
For a survivalist it's more like 'Do I have enough ammo for the guns I own now?' All the guns in the world are useless without ammo. From a utilitarian survivalism perspective a pair of good fighting rifles or even better one per family member of either something AR-15 based or AK-47's then lots of ammo is probably the right answer. (If your pockets are deep I guess .308's are fine) Stocking deep on 5.56 or 7.62x39 to keep the guns you own fed is more important than buying a SCAR/ Steyr-Aug/FN-2000 for fun.
Even aside from ammo should that money be going into food or fuel or a Berkey water filter, or a Titan Ready Water barrel rack system to hold a couple hundred gallons of water or training to use the guns you have?
In short for survivalists you cannot have too many guns but can certainly short yourself elsewhere to get a new toy.