We don't need to buy world class players to get to where we want though. I can't remember the last time the mancs bought a player that was already deemed world class. I'm probably forgetting someone but the last I can think of was Rooney? If we can start producing some quality players from the academy every now and then and target young players in the 10-15m region before they turn into real quality players we won't need to buy world class players to challenge for the league. It may take some time but I really think that the strategy is right if it means when large sums are spent on a player, they should be reasonably (no more than 24 in most cases maybe).
We do need to buy World Class players to get where we want and also to keep there 3 World Class Players we have.
We probably only need 2 more World Class Players and better squad players.
You mention the Mancs, in fairness they have had a strong squad for years and have always until recently topped up their squad each season with a 20-30 million pound signing - now whether that player turned out to be World Class is debatable.
United didn't win anything of note last season nor are they going to win anything of note this season - failure to replace World Class/TopClass players is the reason why (Ronaldo/Tevez)
Arsenal have failed to invest in big money signings instead going with some quality youth players, they have won nothing in 5/6 seasons and are going to lose their best player in the Summer if they don't win the League or Champions League this season. If Arsenal had invested in a few big money signings over the last few seasons (namely a goalkeeper, striker, arguably a centre back and holding midfielder) they would of had some silverware including at least one League.
I don't think we have the time to be waiting around for some good young players to come through because at this rate - Nando & Reina will be gone and Gerrard will be too old.
Also as someone else pointed out Comolli's record is a mixed bag, for every very good player there are has been some shocking players.
We need a few big signings, a few middle of the road signings (who can be young players with potential) and a few teenage kid signings for the future.