Well, he's out of contract summer 2013, so his value should be around 15 mil anyways. So yeah, I'd spend it on him without even thinking about his injury-proneness.
injury-prone or not, I'm okay with Robben playing 50% of our games. he's in the top 10 list.
Ain't happening though :P After the Vidal deal, Bayern will be happy to see him go for free the next summer as long as it's not Juve.