The 0.6m difference in lenght and gain in beam will improve the ride im sure but i think that a hard floor (ali / wood) would be less bumpy and have better stability compared to a air deck. But then this does add weight to the setup and is a whole different issue.
Im not sure on the valves so cant help here.
I would recommend, if you can, to invest in the biggest SIB possible with ali floor. I have a 3.3m ali floor and cant wait to get a 4.8m bad boy.
I recon you should be able to clean out the old ones & if not they just screw in & out!
I have one & it is one hell of a lot of fun for something that is easy & light to carry & fits in the back of the car no problem, but may be better than most Sibs but it ant a Rib!
Also currently I have a 320 airdeck and it is far to bumpy on the sea.
Would a bombard be significantly better?(Less bumpy)
Yes. The Aerotec 380 will perform much better than your current boat. The hull is an entirely different design and is a massive improvement over a flat air floor with an inflatable keel.
I would say that an Aerotec hull actually performs as well as a conventional wood or ali floor with an inflatable keel. Plus it's lighter and has more internal freeboard.