I agree with everything Dave added. In my estimate, I would guess that 80 to 90 percent of the water in the N. Fork Virgin was coming from Deep Creek. If you could find a way to get into Deep Creek higher up in the drainage, that might just be the ticket.
As far as the scenery goes, it is fantastic. In places, the canyon narrows down to maybe 30 feet or so, with vertical walls towering over you 100's of feet. It's basically like paddling through a fracture. The paddle from the confluence with Deep Creek on down is great - getting to the confluence is the hard part. I would also go back, provided there is enough water in the upper 6 miles to actually float my boat. Note: we saw at least 2 diversions in the 1st 6 miles. There are also diversions in the park, like Dave said. These diversions prior to the USGS gage make predictions of upstream flow somewhat problematic.