There's no problem having versatile players but you can't say that 1 player is covering several positions especially when he's already meant to be first choice in another position.
I just honestly think you can live with players who can mix it up a bit at the back. I would rather have two more world beaters than worry about having to put Arbeloa or Carra in the left back position if we had an Injury befall Dossena. I think the top player every game is more use than top benchwarmers, you clearly air more on the side of caution. I would also say that I pressume Deggen when fit to be in serious contention for the RB position.
As for having youngsters on the bench; we saw with Utd last week that it's ok them being there untill they're actually needed to come on and affect the game.
They still won the league though, that is because of the world beaters

IMO we can drop our squad by 2 players without replacements being needed (Voronin and Finnan) and any other player leaving would leave us short of established players in that position. BTW i had a quick count on the BBC's squad lists and i had Utd and Arsenal with 22 first team players.
It depends who you are counting and whether you are baring in mind that some of them would get as few games as our young reserves if they had a bigger core squad. The same list for Liverpool I count 30 players who have played some 1st team footy

Rubbish. From the end of January our side was extremely consistant with a 4-2-3-1 formation and the only changes were Hyypia coming in for Arbelao and occasionally Benayoun for Babel (+ injuries). There were a couple of games around the Arsenal CL ties where 4th was tied up and we rested several players though.
As I said, have a look at the home team sheets. Also bear in mind that the rotation shown was without also having Agger in contention. At the end of the day your central defense needs to stay the same week in, week out.