It really does depend on finances. And the vast majority of players in FM aren't 100% consistent regardless of their stats so there's always room for poor ratings, which makes the game both more realistic and harder when buying players.
Personally I'd offload players with poor average ratings at the end of the season. I've never been a fan of Sissoko myself either in game or in real life, so he'd be the first I'd look at.

Morientes's stats are good though I thought Toure's stats were good too in FM, I'll have to check later.
Though from your success and current players there it doesn't sound like yer doing too badly at all.
It doesn't look like you're playing wingers with just 3 in midfield, so it may be best to look for another AMC to replace/backup Sissoko (note: Gerrard is too good to be squad rotation
IMO 
), a player with good Decisions, Passing, Creativity, and the most important aspects for me when looking for any player - work rate, teamwork, determination, pace, composure, concentration and possibly aggression if possible. There arep layers with all these stats that you should be able to find for a successful Liverpool team by season 2.
Morientes is good, but I'd look to replace him (or low scoring/game ratio strikers) with a real quality striker. Collins John usually does the business for me in my Portsmouth team (if you can shine in that side, yer good
IMO 
), he usually costs 'bout £9million though, but scores quite a few.
Carlos Tevez is very good but very unprofessional so I'd think twice about getting him unless you're prepared to deal with his ocassional hissy fits and poor performances.
There's a guy at Hereveen in Holland if I remember right who scores a fair few, I got him for £5million for Pompey. Can't remember his name at the mo though sorry, but think he plays for them. I definitely know he's an AMR/ST and I think he's 28, though play him as Striker.
Kompany's stats are good (a little too good if you ask me

) but I've often wondered is he reliable enough?