i think it's worth looking at the Utd team of 94 (to me their best team of the 90s) and then seeing what players were still there in their treble year of '99.
Goalkeeper - Schmeicel
Defenders - Bruce, Pallister, Neville, Irwin (their whole back four)
Midfielders - Beckham, Keane, Scholes, Giggs (their whole midfield)
Strikers - Solksjaer
So the bulk of their team were still there 5 years later - quite a few players from their squad had gone, and a few substandard stand-by's were brought in (David May springs to mind) but it was pretty much the same team. Now the advantage is that the team was filled with top quality players - the midfield and goalie in particular. But look at the defence, surely they improved with familarity - if we could keep Finnan, Carragher and Warnock (and a.n.other) for 5 years, surely they'll be solid - especially so with Reina still behind them.
Our midfield - if we keep Gerrard, Alonso, Kewell and Garcia - surely we'll be a better team than if we constantly chop and change.
We have some top class players here now - and we're hopefully going to be signing two more in January. There'll come a point soon when we'll be best off keeping the same team as much as possible, and going back to the old Liverpool system of one oldie out, one young top class newbie in every summer.