I have had quite a few years with the Vivaldi II plumbed version. From a purely functional standpoint the Vivaldi has a lot of pluses for the money. In no particular order . . .
1. line-level preinfusion to experiment with (Personally, never noticed a huge difference)
2. Available integrated on/off timer. This has been great.
3. Very large steam boiler for its price category. Steaming is very powerful.
4. I REALLY like having all the controls mounted high and forward. (when I look at a GS3 I wonder how often I would douse my hand with hot water pushing the wrong button)
5. Volumetric shot control. This has been very precise. I set the single button just to do a backflush, and use the double for espresso.
6. Relatively easy to change temps. Could be easier. Also, you can tweak offset as needed.
7. Plumbed in is great. And easy to do.
8. I was really surprised how much easier group maintenance was with a double boiler is than it was with the Livia heat exchanger. The Livia REALLY baked the residue into the screens. The Vivaldi runs cooler at the head. Makes a surprising difference.
9. Ability to easily switch off the steam boiler and just run the group boiler (actually, this should be near the top of the list!)
10. Height of the unit is nice for those of us with lower cabinets.

Build quality is good, but not what I would call fantastic. A few rattles here and there, but you can track them down and stop them with a little tape or foam. Plastic sides are pretty practical--no dents when you accidently hit them with a portafilter, for example.

Regarding upgraditis, yes, it has hit me too. For me, I am really tempted to upgrade to the LMLM. I would give up a LOT of features in the quest for possibly better espresso. Wish I could compare espresso cups side by side, but that's not very easy.