Even though I'm only at the start of the 5th season now (whereas I was at the start of the 4th season when I made this thread), I have already made significant gains.
Yaya Toure was at the end of his prime years, as he was 31. I sold him for 7 million pounds and bought Jack Rodwell for 22 million. Rodwell is as good as Toure, but is 8 years younger, so I think it was a pretty good deal to only pay 15 million pounds more than I sold Toure for.
I bought Messi for 115 million pounds. As of now, he is going to take over Balotelli's spot at AMR. I will try to loan Balotelli out (though so far no luck on that. If I can't loan him out, I'll have to play him some at Poacher/AMR/AML to keep him happy here). Tevez is 30 now though so I only have a couple more years left of him, so after a couple years, he will be replaced at Poacher with Messi or Balotelli and the other one will reprise his role as AMR.
I bought Babacar for 20.5 million pounds. He is an eventual replacement for Dzeko, who is now 28. I will try to loan Babacar out until Dzeko is past it so Babacar doesn't get disgruntled by a lack of playing time. Either that or I could simply sell Dzeko now and start using Babacar right away. I'm not yet sure which is the better idea. Babacar is already at his peak, so he isn't a step down from Dzeko. This makes me think it might be best to sell Dzeko now while I can get a lot for him and just play Babacar.
In any case, I also started on the next generation of my team (ie. regens) as well. I bought a very promising 17 year old Italian striker who will eventually be a poacher-type. I bought a 19 year old Brazilian center midfielder who excites me because he has great passing/technique/dribbling type stats you expect for a playmaker, will score goals due to a very high long shots, will be great in defense due to a 16 in marking, AND is 6 foot 4 which will help a lot in keeping possession. I also got an extremely promising 16 year old Brazilian AMR and a 17 year old Brazilian Right Defender. If I sell Dzeko now, I can probably get the money to buy an immensely promising Spanish Left Defender.