Not sure if you have rebuilt and thoroughly cleaned the carbs yet, but that did WONDERS for my mileage. I was astonished at how much crap had gotten into all the nooks and crannies.
As a part of rebuilding the carbs you will also have to rebalance them. In getting the rebalancing correct you will also likely get it to run much more smoothly (both at speed and at idle).
I also now understand my bike much better now that I have had the carbs apart. The black magic that goes on inside a carb is much less mysterious now.
So...um...rebuild yer carbs.