I myself am torn between unifying them or not. As stated, Raw is the supreme of the two shows because it features superstars from both shows. Smackdown, on the other hand, rarely features Raw superstars. Quite frankly, most significant developments on Smackdown are replayed or summarized on Raw, so you could realistically never watch Smackdown and still have a pretty good idea of what's going on by just watching Raw. (Although I have noticed that the Cody Rhodes/Goldust feud has yet to be addressed on Raw.)
My point is that it's very clear that the WWE Championship is the more prestigious of the two. But WWE rarely acknowledges this. Even when ECW was around, I remember John Morrison becoming ECW champion and WWE.com advertising it that ECW was finally considered an "A" show. (or something to that effect. This was over four years ago).
Ultimately, while I would be okay with them unifying the two belts, the World title is more or less a prop right now, and I'm okay with that as well. I mean, if there were only one belt, what would Daniel Bryan be feuding with Mark Henry and Big Show over? Bragging rights? And it really wouldn't be the same if they were feuding over the Intercontinental title. I feel like the World title is at the same level that the Intercontinental title was in the late 90's. However, the values of the IC and US titles are about the level of the European and Television titles, so the whole title scene is just messed up and I'm not sure the two world titles are the biggest problem. The fact that Jack Swagger is walking around with the United States title is a huge problem to me, because I don't think he is anywhere near the level (although I was fine with Zack Ryder having it, because at least he is over with the fans).
So in closing, ideally there would be one world title and two lower titles. But I think accomplishing this is far more complicated than just unifying the two world titles. If anything, they should unify the United States and Intercontinental titles, and then make it clear that the WWE title is the "main" title and the World title falls somewhere between the WWE title and Intercontinental title. Heck, rename it if you have to.