I didnt thnk about the shows being different.
Allure already has the Dreamworks 3D movies and such, and it has Chicago instead of Hairspray.
I actually liked Hairspray better than Chicago, but that could have just been me (I was tired that night). The thing about Fosse is that you need the best dancers in the world to pull it off.
I only stayed through the first scene (which seemed like it went on forever).
BUt, you could try the different restaurants if you change ships, too. Only the ports would matter.
I do think the ships are interesting enough that you could do two weeks on one or both and then also do the other one.
Some people (who have never seen Oasis) have already decided they don't like it. On the other hand, most people who have seen say it is amazing. I am in that camp.
I also just like the look of Oasis a bit better than Allure. Its a little classier.