I would think the Saudi League is equivalent to Double-A baseball in soccer terms. Sure they have money to throw around, but any good player wants to be in the EPL, or La Liga, or the Bundesleague. Much better exposure. Who cares if Riyadh beats Dhahran?! As for his future in Europe, he is 37 and nothing can change that. He could probably get a small fortune from an MLS team though.
It seems like the Saudi League is worse than Double-A. A lot of players in Double-A make or almost make MLB. Is that true of Saudi League?
Ronaldo is very fit for his age. He could play in the MLS for several years.