Well, if you don't have OOO, do so now.
I didn't like how much Oblivion changed whenever I leveled up either.
OOO is much more static, and I couldn't live without it now.
It made Oblivion a bit more like Morrowind, and so far I have had no problems with OOO.
As for the adventurers, I'm pretty sure they were always in the game.
I haven't noticed them in any areas I hadn't seen them before, so my guess is it doesn't add more or them.
But, I could be wrong with that.