I had the opportunity yesterday to do a "ship tour" of the Regatta while it spent the night in port. They hosted one of our local travel agencies as well as the local AAA office and they, in turn, invited interested customers. Now this was one of their old, small ships, but I really noticed several of those items in your review.
We started out in the lounge, and it sure was dark (granted, they were showing a PowerPoint presentation, but...). Even the stairs going up from the gangway level to the lounge were like an old hotel. We then split into small groups to see a variety of cabins. I noticed what you meant about size. I thought it was about European riverboat cabin size on some of those. I haven't been on VO yet (we are going this October), but we did do the Mississippi which has the same categories of cabins and we loved our PV. The V-Miss is sort of "VO Light" in its layout and we loved it. Last night I was looking at the website for the VO ships and we just loved the Scandinavian design.
They did take us in for a very delightful lunch. If I was on an Oceania ship for any length of time, I'd have to spend a lot of time in the fitness center.
It would have to be a very good itinerary that would woo me away from Viking.