I'm at a similar decision point and I'm underwhelmed by Xerox and their supply chain incompetence. Ricoh 9200 is current my top candidate and has similar specs to the Iridesse at a substantially lower price, but without specialty colors that I don't need. The specialty colors require a...
https://www.usa.canon.com/internet/portal/us/home/products/details/production-printing/color-sheetfed-digital-presses/imagepress-v1000
There aren't a lot of specifications released, but it looks like a competitor to the Xerox Versant 280 and Ricoh 7200.
We've had a couple sales reps look at our current volumes and tell us that the Ricoh 9200/KM 12000 are "overkill".
I was recently told that we would have to prove that we'd have enough volume to be *permitted* to purchase a 9200 or Iridesse. I'm suspicious that it is a tactic to spike the price...
x-Digital in California is a Xerox refurbisher who probably has access to Xerox firmware. You might ask them if they could help you for a consulting fee.
Your Duplo 618 should allow micro adjustments to get the print assets right on the folds, but you have to start with an accurate file and tight front to back registration. My setup is almost the same as yours- Duplo 646 and V3100.
To attempt to clean the heads:
1) initiate a knife change and open the cover. The knife change will unlock the head so that you can move it.
2) soak a lint free rag with windex and put it under the head and let it sit for a few hours and then run a heavy cleaning. See if that improves your print...