I own several Sigs. My fav gun is a P226 and I have several thousand rounds through it. I am a traditionalist when it comes to small arms and I have resisted as long as I could to move to the 21st century but eventually I started looking for a polymer framed partially pre-tensioned striker pistol. I have tried the Glock and the S&W M&P, both very good pistols but they didn't do it for me. Then I tried the P320 and I bought one on the spot. That being said, the P320 is nothing like a P226. They are two radically different pistols. But I think Sig hit it right with the P320. It sits low in my hand, I have a very good grip and I like the trigger pull and the recoil and how I can take up quick follow-up shots.
With regards to your question about barrel swap, I am myself not a fan of it. Once my pistol is right where I want it and runs smoothly and reliably and hits where i want it to hit, I don't like making changes to it and having to start all over again and build up confidence. If I want a different set-up or caliber I would rather have a complete other pistol.
I hope this helps you.