I hardly noticed any improvement in picture quality to be honest if any - but to me images over HDMI and component are almost identical too .. (as they were on Dish) If you were only considering the switch because of PQ - it would probably not be worth it - especially if you would not be interested in the HD that they have that Dish does not have yet.
If Dish has everything you need ... you are probably right to stick with what you have right now.
One week in for me and so far it was worth the switch for the on-demand alone.