Henry, Vieira, Gilberto, Flamini, Cole, Reyes, Pires, ffs even Hleb and SOL walked out on Arsenal and asked to leave rather than Wenger upgrading.
I don't think Flamini was the best player in the world, still isn't, but he's a freaking monumental leap up from Diaby/Denilson/Song. The rest were all significantly better than the players who they were "replaced" with.
Personally I'm not convinced that Reyes was better than Van Persie but I suppose one can always argue the toss about who exactly replaced who, especially as it wasn't a case of them leaving and joining at the same time.
I think the main problems we've had in the transfer market are:
1) Letting 'irreplaceable' players in Vieira and Henry go at rock-bottom prices, £30m the pair, when had we cashed in a year earlier you could have doubled that number. Even if 'irreplaceable' is too strong a phrase, they were certainly irrepleceable for the fees we sold them at.
2) Lack of focus on weak positions i.e. DM, instead pursuing the usual Wenger Boys (tricky forwards/AMs - by which I mean if you have a squad with RvP, Arshavin, Walcott, Vela, JET, Fabregas, Nasri, Rosicknote etc you can't play them all at once)
3) Failure to replace backup players like Flamini, Edu, Bergkamp etc with equal quality as you say. Flamini was a weird one because he waited around a few years for his chance, finally got it and then promptly legged it.
4) Overemphasis on DOB i.e. anyone born before the 80s is shipped out or given a 1 year deal e.g. Gallas, Pires etc
5) Allowing 4 of the best 5 CBs to leave in the same summer (Gallas, Campbell, Silvestre, Senderos) leading to panic buys like £6m on Squillacci (ok maybe 'panic' is too strong but clearly more thought/money should have been thrown at the situation)
Not all bad of course and I think Wenger still make some good moves in the transfer market. But one question you would have to ask is in the past couple of years how many genuinely great deals has he pulled off - Vermaelen maybe but haven't seen enough lateley due to his injury.... Arshavin in a good player but wasn't cheap. Nasri was 3 years ago now. Certainly no mega-bargains like Cesc, RvP, Toure, Anelka, Clichy etc.
In terms of 'upgrading' the bench one thing I get confused over is bearing in mind your obsession with wages why we would be looking to do this. Surely the solution for bench players must therefore be putting cheap/youth players there not top quality. I.e. instead of Chamakh and Walcott we should have say Vela and JET on the bench.