I think he is all we can hope for in a back-up 9. I like that he is young rather than a oldie who we would have to replace at the same time as Suarez.
Valencia has been quite a mess both on and off the pitch, and here he would at least meet some certainty in the defined playing-style and less chaos in terms of players in and out. IMO he has already proved much more than Munir, but if he has reached peak-level the price is too high. Therefore I think we bet that he will do better here, than at Valencia (which would make him worth the money). Nothing is 100% certain, but the conditions for him to be a success are all here.
If Munir is part of the deal and ends up at Valencia, the whole thing becomes somewhat bittersweet, as Valencia clearly isn't an optimal place to develop right now. I certainly agree that we shouldn't trash La Masia-products, but loaning Munir out wouldn't be bad for him - if he goes to Celta e.g.. Valencia makes me doubt a little more, but all in all I'm still in favour of the deal.