The view of Vernal Fall from the footbridge is somewhat obscured by trees, but a few hundred meters up the trail, it gets considerably better. There's no need to stop here - in my opinion, you haven't really been on the Mist Trail unless you've hiked for enough to feel the spray from the falls - but this certainly isn't bad, and it spares your knees the hundred and some stone steps that take you up the last stretch to the top of the fall.
If your knees are in fact a serious obstacle to your hiking happiness, you can detour onto the longer but gentler John Muir Trail shortly before you reach this spot. If you go downhill at the first fork in the Muir Trail, you'll emerge back on the Mist Trail a little ways above Vernal Fall. From there you can go back down the Mist Trail a quarter mile or so to see the view from the lip of the falls without enduring any more steep verticals. The trail map might help make this clearer.
The vast rock poking up into the sunset behind Vernal Fall is Liberty Cap, which you can see more clearly here (that's Nevada Fall, not Vernal Fall, in the Liberty Cap photo. Nevada Fall is two miles [three km] upstream from Vernal Fall).