He did make a load of signings that didn't work out. Like city later, Chelsea signed less players but spent significantly more on those players and the cost of the contract too.
Where Rafa for me went wrong was just buying too many cheap players with PO tential 
more of Torres ilk would have been welcome. We had a complete 2nd tier of players that never made it at all. I mean Veronin?

Ngog Pongolwhatever, none of these were future CL PL champions and never would be. Way too many "stock" players, it was almost like panhandling
Rafa was not and never has been brilliant in the transfer market but then again,
stay in the game long enough and you'll make a bunch of signings that didn't work out just like every other manager. Wenger has done alright. Big sham put together a decent Bolton outfit for buttons, Moyes at Everton not bad at all with the purse strings.
Fergie has probably blown more money than Moyes has ever had to spend if you wanted to look at it that way