The Galaxy Nexus doesn't have qhd resolution (540 x 960) it has 720p resolution (720 x 1280). Anyways, if you land up waiting for a phone of which we're not even sure if it will come to Sprint (chances are it will though), it won't be much further down the road until you will see the first quad core phones being introduced at CES next January.
This is a very personal decision, is your current Epic too slow? Are you tired of the keyboard? Do you have apps that don't run great on the Epic? Do you just want a bigger screen with same resolution as your current Epic? Are you tired of Touchwhiz 3 and want some Touchwhiz 4 action instead?
I personally went from an Evo 3d to the ET4G because the 3d didn't seem to be a huge step over the 4G, it just looked too familiar, the overall UI was still kinda jerky, I didn't like the carousel thing that prevented live wallpapers to run properly, and because my particular unit (the second one) gave me all kinds of strange problems. The Evo 3d played the games the 4G couldn't handle, and that was about it. So I went to the ET4G and couldn't be happier, it's an awesome phone, but it also brought a ton of changes to the scenery with a totally different UI and finally having none of the lag I experienced with the Evos. So when you go from the Epic to the Epic Touch, you might feel the same way as I did going from the Evo 4G to the 3d. Combing that with all the exciting news about new phones coming out next year, and you might regret your decision. As far as the Galaxy Nexus, yeah, it's fast, but not much faster in than any of the other current phones out there. It does have that 720p screen and the fastest update support being that it's a Nexus, but again, it's "just" a dual core phone.
Just a few things to think about...