Me: "I already have the Connect:Amp. I don't really need to upgrade."
Also me: "Something new from Sonos? TAKE MY MONEY."
In all seriousness:
If you have the coin to upgrade and plan on sticking with Sonos long term, I can recommend getting the newer AMP.
My B&W CCM382 ceiling speakers never lived up to their potential with the older Connect:Amp. They sounded OK but unremarkable. Powered by the new AMP, they carry so much more punch to them. There's a richness that was simply was lacking in the previous setup.
Pluses: modern design, expansion capabilities (up to 4 speakers instead of 2)
Here's what I should have known but didn't: swapping out amp devices means reconnecting all the speakers and services that were tied to the old amp. That took longer than swapping out the hardware.
If you have neither and you're deciding between Connect:Amp or Amp, spent the extra $100. All day long.