Perhaps so. I don't personally think its great to keep a player against his wishes for too long and I can certainly see and 100% understand the reasons behind Modric wanting to leave. If he doesn't act too badly ie become Berbatov and especially if he goes abroad, I wish him every happiness.
Can we though? How much does 30 million actually get you in today's market? Last summer, AOC went for 12-15 million, Mertesacker and Gervinho for 10 each, Mata for 26 million, Lukaku for 20 million, Ruiz for 10 million, Henderson and Downing for 20 million each, Aguero for 35, Nasri with a year left on his contract 25, De Gea, Jones and Young all for around 18 million each, Palacios and Crouch for 20 million

, etc etc. 30 million, for the most part, doesn't get you that much anymore.
There's a good reason why the top clubs stay where they are and the clubs the level below, ie Seville/Aston Villa/probably us once we sell Modric and Bale and have all that money to play with stay where we are. They keep their top players. And buy ours. We sell them. Eventually, you don't find the players to replace them anymore and you fall back into mediocrity again. You can do it maybe once, twice. A few more times if your scouting department is great and you get a bit of luck. Not more.
We're much more likely to find the next Pav and Zokora than the next Berbatov and Modric. There's good reason for that, because otherwise the buying club would usually just buy that player instead.