I was possibly not clear on this the first time: I think the existing infrastructure of Catalonia is more developed than that of other regions, thus it deserves less investment than those other regions, per capita. With your additions to just how complex the infrastructure issue is, I suggest on some fields this could be managed: say, there is reliable statistics on social infrastructure like canalisation, you could make investment in that field an inverse function of the ratio of already canalised homes. (Do you know anything about how social infrastructure spending, as opposed to transport stuff, is divided up now?)

On the other hand, say, metro stations or bus routes into poor suburbs could be financed in a population+income-based way that ends up giving more to Madrid and Barcelona than other areas.

_{*Lunatic*, n.
One whose delusions are out of fashion.}