Another Cuben Duomid owner here, since this spring; I took it on a three week trip to Norway where it saw plenty of sun and rain. In addition to the Duomid I have the Sean's Oooknest inner. Good combo, although in retrospect I probably would have liked the slightly smaller Oooknest Nano better.
Duomid vs Solomid: when using an inner(net) I would definitely go for the Duomid, I think the extra room due to the larger depth (width is the same) will be really noticable and welcome. When using a bivy the Solomid is enticing because you can use 2 trekking poles in an inverted V, so no center pole that gets in the way, and less deflection of the larger sidewalls when it's windy.
Cuben vs silnylon: cuben does not stretch when wet (claimed and witnessed after 33 hours of continuous rain) so there's less chance the outer will touch the inner. Which was one of the mayor annoyances of my previous tent, so an argument I used to convince myself that I needed cuben ;-) For weight alone, not worth it IMO. Oh, and if you have never seen cuben before and you take the Duomid out of the (silnylon) stuffsack it comes in, you'll probably be disappointed: just a bundle of wrinkly, translucent, cheap looking plastic...
While cuben may not stretch, the side panels will deflect even in moderate winds (I measured 18 mph gusts) and you may want to pitch the Duomid close to the ground. When pitching low the smaller Oooknest Nano would leave more space between the inner and outer.
As for modifications, I asked Ron about an extra tie-out in the front so you could leave the right panel closed while opening the left panel. It was doable, but not recommended because the fabric near the zipper on the right panel was not as strong. So I did not order this change, and in hindsight have not missed it.
In wet weather you can open the right panel partially by opening the zip upto the reinforced press studs at around 16" from the bottom and flipping it onto the sidepanel; it will stick (the cuben at least) because of the wetness. One thing I would have liked is to be able to open it a little more (say half way). But if you do so without modifications you may put too much tension on the zipper (or maybe not, I should ask Ron).
Anyway, great shelter; even (especially) in prolonged rain.