I think that many first time snowshoe users are surprised how far they sink into the snow. Last weekend, I was out with a "first-timer," my friend, Emily. She was borrowing a pair of my snowshoes and she made the exact same comment. I think most people imagine you just float on top of the snow with snowshoes, but in reality, it doesn't really work that way.
If there's powder, you're going to sink down a few inches. A larger snowshoe with more flotation may help, but you're still going to sink a few inches and may lose some maneuverability. Also, if you're wearing snowshoes and you don't sink at all, the snow may be packed enough that you don't even need to wear them anyway.
The real test is to take your snowshoes off and see how deep you would sink without anything on your feet. I did just that to demonstrate to my friend and I sank down to my crotch.
So, overall, longer snowshoes may help a bit, but the question will be how much will they help and is more flotation even really necessary? In my estimation, as long as you're sinking less than a foot, you're doing alright.