I agree, there's no advantage to be had from an increased pixel density. If anything it will only tax the GPU more rendering a slower experience. I got the first Retina iPad and I'm disappointed by the slowdown I've experienced since later iOS 6 builds and iOS 7 where things have become seriously frustrating.
Work on better longevity Apple. The kind of speed I experienced on iPhone 5 with iOS 6 was wonderful. So fluid and reactive. Now I know with the next few iterations of iOS 7 that I will be dragged to hell.
What would your experience with the first Retina iPad have to do with the performance of a future iPad, which presumably would have a beefier GPU?
Especially since you only mention the later iOS 6 builds and iOS 7. If it was working okay with iOS early builds, then lagged with later builds, I wouldn't blame Retina for the problems. It already was Retina when it worked well.
Do you want Apple to reduce the resolution and put a less capable GPU in the iPad 6?