Here you are talking about MPEG2 vs MPEG4 compression, which on paper looks better and should offer better compression rates but as of right now you will really not notice any huge difference regarding picture quality. DishHDLite is really not only directly related to MPEG4...it is just way E* is preserving its bandwith capacities trying to cram more into less.
Until they "up" resolution and bitrates and move to TRUEHD in my option, the type and quality of your TV and cables could more affect your picture quality than type of MPEG or move to 622 alone.
I would look at this just from the perspective that 622 is future ready (all new channels they add with be MPEG4) and it is pretty good DVR so you could move now or wait...