all of the above, plus...
I figure at least that if I were to sell a gun I already have, I'd get a LOT less back than what I paid for it. Hardly worth it then to get rid of a gun, even if I see something that'll work better for me... better just keep that old one around for a spare or the "what if" scenarios other people already discussed.
You'll almost certainly keep seeing firearms that'll serve some purpose better than what you already have, so get it! Sort of the 12 days of Christmas but in reverse...
For years I had a couple of 9mm service pistols that stayed in the house, then when I decided to CCW I needed something smaller, so I got a 380 that could fit a pocket holster.
... then I saw and bought a compact 9mm for pocket carry... but kept the 380 and the other 9's.
Then I came across a value-priced .357 snubbie and I wanted the increased knockdown power of .357, so i got that, but kept the compact 9, the 380, and the service 9s.
Then I wanted more knockdown power for HD, so I got a 12 gauge, but kept the .357, the compact 9, the 380, and the service 9s.
Then Katrina hit NO and LA, and I worried about a SHTF scenario and not being able to keep marauding hoodlums at bay with my pistols.. so I got a Mauser K98 collectable but I shoot it. But I kept the 12 gauge, the .357, the compact 9, the 380, and the service 9s.
Then I heard about SKS rifles, and thought "could use the increased firepower, and 8mm mauser is kind of hard to get without the internet", so I bought an SKS. But, I kept the Mauser K98, the 12 gauge, the .357, the compact 9, the 380, and the service 9s.
Then I had to get a .22 plinker to practice with, so I could "save money at the range." So I got a 10/22, but ... kept the SKS, the Mauser K98, the 12 gauge, the .357, the compact 9, the 380, and the service 9s.
I think I've done well to get all this past the Finance Committee, and I'm optimistic I can slide some sort of AK clone (a low-end WASR will be dandy for me) you know because in a SHTF scene I might need more firepower than the SKS can lay out. And I've got a nice pile of 7.62x39 anyway... but I'll keep the SKS, the Mauser K98, the 12 gauge, the .357, the compact 9, the 380, and the service 9s.
One other side benefit to building up a collection in case you're worried about SHTF, I think, is that if things go badly enough that money's no good, think how much you could barter a rifle and say 200 rounds for it for! You'd better start off well-equipped because there's no going back to Gander Mountain or even Walmart once the balloon goes up. Clean them out of shotgun shells and 9mm BEFORE it happens!