The 3D cinema was roughly on Hydro's site, but did close a few years before Hydro's construction. You don't really see those 3D cinemas in domes anymore. I'm pretty sure Thorpe used to have one as well as, obviously, Alton Towers. I guess they've just become out-dated.
As for Bounce, it did indeed replace the assault course and, again, I guess Oakwood just saw the assault course as something that was outdated and better suited to a country park rather than theme park setting. If this was the case, I guess we're lucky that this attitude didn't extend to the likes of Bobsleigh and the Boating Lake.
On a different topic, does anyone know if the Bowling alley next door to Oakwood (and run by the park) still operates? I've driven past it a few times at various different times of day and it looks pretty shut down