Hey, I saw FE in the theaters and then bought it when it came out on DVD, (few years ago). It was my first rfftrax just because I could listen to it right away as it was the only DVD I owned for a rifftrax.
I loved the riffing. I wasn't offended because I liked the Fifth Element as a movie. There WERE very very goofy moments that needed to be made fun of. I thought it was well directed and had some nice sci-fi elements (no pun intended), and the special FX are still great, but the story did need a bit of polish. It was like a first draft, really. And, there were some very odd choices on the part of the director and the actors alike.
Mike pointed out stupid things I never noticed before, like the squealing tires on the flying cars, or the really bad costumes that I had never looked at too closely but, he's right, they are silly as all hell.
In summary, to your point, I don't think your concerns are very valid. Certainly not universally so, at any rate. I think it will do well.