Crackdown's aiming is similar, but it's not nearly as good. For example, you can't do drive bys at all in Crackdown, the manual aiming can be extremely wonky at times too.
You can see those things in your character screen. In GTASA all you have to do is press L1 and the stats pop up. The more muscle you have, the stronger you are; the more the stamina you have the further you can run and swim;etc. It was not a number, but it was a bar.
Maybe I have not played enough of Saints Row (I've been busy with other games). I'll play more of it after I'm done with my current onslaught of games. I really really like the game though. I like sandbox games a lot, and it's one of the better ones that isn't GTA.
You're right that GTA isn't comparable to AC....yet. We don't know if it will or not. Remember that how many people appear on screen depends on the time of day. Also consider this, in GTA you have vehicles. It would be extremely annoying trying to drive through herds of pedestrian cattle when you don't want to be noticed by cops. I think if GTA doesn't have any many people as AC, it will be a gameplay decision, not a technical decision.
I guess I just sound like I'm some crazy fanboy at this point, but I don't care. I have had much more fun with the GTA games from last gen than any of the current gen sandbox games combined. I don't know if it's nostalgia or what, but I've played through the last gen GTA's MULTIPLE times, more times than I can count and I still don't get bored. I'm not so sure if I can do that with current gen sandbox games.