delle alpi had running tracks and the stands were far from the pitch, it was worse than olimpico in rome is. I know juve stadium can expand to ~55k, read it somewhere, the whole infrastructure around the stadium is good for that.
anyway, looking at other big clubs, lets say real doubles the income from tickets, barca almost triples, given their matches might even cost more and people still willing to pay. let alone MU or arsenal, people fills the stadium no matter the ticket price