Honestly I wouldn't be opposed to a change in the leve system, though removing the leve limit would raise issues with the upsized versions of the combat leves.

As for the crafting, I guess they didn't want to make levelling a crafting skill as straight forward as spamming leves. As it is, spamming leves is by far the quickest way to level crafting, particularly if you have gil to burn. Still having a turn in system which gave lesser EXP rewards outside the leves and the GC should be ok like the collectable system like you said. After all it works above 50.

That's not a bad idea and probably more workable. 15 to 50 collectables.