Barry,
We have a 2010 2551 with the sofa/air bed.
I don't know if you can fit the new sofa/air bed in your 2007, that would be a question for the factory.
The dealer we bought from had a 2009 model with the electric sofa bed and a 2010 model with the sofa air bed, we were able to directly compare the two.
Regarding comfort in the sofa position, the new sofa air bed was much more comfortable to sit on, probably because it is built primarily as a sofa whereas the cushions on the electric sofa bed serve as both sofa cushions and bed mattress. Agree with the post above that the air mattress is not that comfortable to sleep on, but for us it is only used once per year for the grandkids. Depends on how often and who sleeps on the sofa as to whether the sleeping comfort is an issue.
Another big difference we noticed was that when in the sofa position, the new sofa air bed stuck out from the wall 8 inches less that the electric sofa bed, a big deal for space in a small rv. Confirm that dimension with the factory if you decide to change it out.
Bob