Quality is quality. It's good to negotiate the price down and all, but when there is interest from other big teams then you go on with the market.
Tottenham paid £16.5 million for Modric when they bought him from the Croatian league. Firoentina paid some 10m eur for an 18 year old Jovetic bought directly from the Serbian league.
We shouldn't wait, and we don't have the money to wait, for a player to prove his world class in a CL final or for big teams like Real, Manchester etc before we buy him.
If we decided to buy Krasic as one of our main, or the main transfers, then it means that we saw quality in him and that we need him. In such cases overpaying is fine.