I was not disappointed with not having more room, the seats were actually quite comfortable and I don't expect to get something I did not pay for. Looking at the seatmap we were right in the middle of where the extra legroom seats where, I did not look any further and you are right that it is just a small section.

I guess I had high expectations from Virgin that did not pan out. First, they canceled our flight from IAD about 4 months out, moved to EWR. That flight was cheaper in miles than the original flight, they did not volunteer that information and I had to push a bit to have the miles returned. Then they canceled our nice seats on the side towards the front, put us further in the back and refused to reinstate them (had them printed on my boarding pass from home). Eventually I believe it was weight and balance, no problem with that, but at the checkin desk they did not tell us and basically said this is it, these are your seats or you don't fly. They did not tell us the load was maybe 20% overall or give us choices of seats. Service was ok, but not overly welcoming.

In the end, they got us over the pond safely, the plane was in excellent condition, great entertainment system, luggage came out fast and overall it was a good experience. We still got very good value out of our miles and for US-UK I'd do this again without hesitation. I would just have a better idea of what to expect in terms of attitude.