that's not the right thing to do imo. I mean he's 20 years old, and his price won't ever drop again for the next 10 years (probably). Rakitic is the typical kind of player you could gamble on. His 1st year at schalke was maybe not that stunning, but it was far from bad (in 29 games, 3 goals, 10 assists, and i believe he never played the full 90 minutes. very often coming off the bench in ~70st minute).
But i agree that we're surely not in a position where we can just buy random players. First of all, we should very precisely look where this guy wants to play, and where his strengths are. I think the only position we could use him is as AMR, as a sub for camo. The fact that he's versatile is useful here, because we have marchionni and giovinco coming up in similar positions.
Either way, his age is his big plus. If we bought him now, we'd be sure to profit out of him (one way or the other, either by developing the next Camo, or the other, by selling him afterwards if he doesn't succeed). Waiting for next year would be the wrong thing to do, because then we'll have the usual suspects (chelsea, madrid, inter, ...) to compete with...
It's all a question of risk-taking, and if we have those 15mio left for him. at the end, i think he will NOT be sold by schalke (at least not for 12mio) and then, we have other spots to cover first, and our budget is limited. I'd doubt that we sign both alonso and rakitic. That would make +30mio euros only for our midfield... seems exaggerated when we have our problems in our defensive row