The thing with Arsenal is that they have lost Flamini who was awsome for them all last season, they will lose Hleb who has been great for them also, I can see him bringing in young players but I can't see them bringing in two players with as much quality as them two. So I can't see them being any better for sure.
I think Chelsea are in a dilema which I think you see quite often on the continent with teams like Real, Barca and some Italian teams who change their manager and too many other playing/caoching staff too often and it only leads to inconsistent success. They will still be one of the teams to beat but I think they are going to be less of a force this year than they were last. Which goes with you point that we cannot afford to make too many changes.
Man U are the team to beat, no doubt, I hate them but respect them, I hate Ferguson but admire him for what he and they have achieved over the last 10/15 years with green eyes. However wether Ronaldo stays or goes I can't see Man U getting the glut of goals from him this coming season and with Giggs and Scholes beginning to slowly bow out I don't think they have the quality and/or experience to replace them. Defensively they are awsome, Attacking they are great but I think their midfield is either a little too long in the tooth, not good enogh or a little to inexperienced. I will be interested to see if they improve their midfield or not as this will make all the difference.
I am always the optomist so Come on Rafa and the Migty Reds lets at least take it to the last day of the season and show we are true contenders.