Have done three trips to Raja Ampat on three different boats and find you pretty much get what you pay for. Damai I was the most expensive and probably the best overall experience. Huge rooms, excellent food, excellent guides and an overall attention to details that I have never experienced on any other boat. Dewi Nusantara was a close second, a much bigger boat with many more divers on the boat, but still a very "luxury" oriented experience. Really the difference was in the details, overall an excellent experience. The third boat Ondina was significantly cheaper and the dive experience was still excellent - food was much simpler, the accommodation less luxurious - everything about the boat was just a bit worn. Serviceable but tired.
I would do any one of the three again in a second. The dive experience is what I am after so the added luxury touches are not necessary for me and I would put the $ toward my next trip. However, there is a significant difference, and if you enjoy the added extras and want the "luxury" experience then Damai and similar will not disappoint, and really - when you look at the overall cost of these trips the difference in price is not that much unless you go with the really budget boats.
One of the down sides to the Damai was that there were only 9 guests on board and as the only single aboard it was a bit like being a third wheel at times. Everyone made sure to include me in conversation and not complaining at all, just an observation.
Have done two trips as a single diver on a trip that was an addition to a group dive. One a club dive from the UK and another a group from Hungary. Language was certainly an issue on the Hungarian trip. They certainly tried their very best to include me and the one other non Hungarian diver in conversation and the group in general but the language barrier made that very difficult. Same thing with the UK dive club, but there was no language barrier so it worked much better. If I had a choice I would prefer a "non club" group over filling in an unsold spot on a group trip - even without the language barrier.