When I first started out, I wanted to try EVERYTHING so I could make the best educated decision about what I really wanted.
Since I've gotten a little older, while I still believe the variety is the spice of life, I also believe if it ain't broke, don't fix it.
So now, I do a little of both. I have several guns that are the same make/model, but different cartridges, and I have several guns that are the same cartridge and style, but different brands. Some guns I have the same brand and model, but different "options"
For example:
My fiancee and I both have Benelli Supernova 12ga's.
I have 3 Ruger Mark II/III's .22lrs and my fiancee has 1. One with a pac-lite upper that I built, one standard barrel, a slab-side "competition" model, and a fluted heavy barrel "hunter" model.
I have a Wilson Combat UT-15, a Bushmaster Superlight Carbine M4, and an Armalite M4 carbine.
I have a Ruger Superblackhawk .44mag and a Taurus Raging Bull .44mag.
I have a Marlin 1985 Stainless Guide gun .45-70 and a Marlin 1985 Cowboy .45-70 (20" vs 26" barrel).
My fiancee has a Savage 12 BSEV .22lr, a 12 BVSS .223, and 12 VLP DBM .300wsm.
My primary CCW is a Springfield armory 1911 Micro-Compact Bi-tone .45acp, while my fiancee carries a Springfield 1911 EMP bi-tone 9mm.
So yeah, I like having different guns for different purposes, and I like trying new things, but when I find something that I really like, I'll stick with it.