Depends upon what you shoot....
If it's mostly action and sports, then either stick with the 50D (which is quite capable) or go to the 7D. You could expect a slight improvement in your keeper rate with 7D, just don't expect a lot. I shot with three 50Ds for a while and got 94-95% of my shots acceptibly within focus. Switched to a pair of 7Ds and, after an initial struggle to learn to use them well, now get probably about 96-97% of my shots acceptibly in focus.
It's not the 50D. With either7D or 50D, lenses make a bigger difference than the camera. Most of what I use (all of what I use for sports/action) are reasonably fast focusing USM lenses.
5DII is not a good camera for action/sports. I use one for portraiture, landscapes, architecture, some macro.... One Shot mode stuff. Not AI Servo shooting.
If you want a full frame camera that does both, you'll need to make the stretch to the 5DIII... or perhaps the 6D (supposedly a bit better at AI Servo work than 5DII, but not as good as 5DIII).
The problem with switching to full frame is that the cost of the camera is just the tip of the iceberg of the expense. You are also going to have to replace at least three of your lenses. The selection of lenses for FF is smaller, too... And the lenses for FF tend to be bigger, heavier and more expensive. I was lucky... I shot Canon film cameras long before I shot digital, so I already had a bunch of full frame capable lenses. I only own one crop only lens (a Tokina 12-24/4) and when I added the 5DII to my kit a few years ago only bought one lens specifically for FF (135/2L).
Full frame can be nice, but crop cameras are pretty darned capable and can be a better choice for a lot of people and will serve most purposes very well. And the 50D is a reasonably high resolution and fairly capable model. Sure, 7D is an upgrade... but really not as huge a step up as it might seem.
Basically, I'd suggest keeping your 50D a while longer and start get some better lenses. If you decide to stick with crop cameras, continue to use EF-S lenses as they are a very good value. The 15-85 is excellent. So is the 85/1.8 (assuming that's the lens you reference in your sig). Replace the 55-250 with one of the 70-200s. Worlds of difference in focus speed and accuracy. If at all possible, get one of the IS models. IMO, it's worth it. Check out the size, weight & cost of the f4 and f2.8 models to decide between them.
If you are determined to go to FF, I'd suggest to still keep shooting with the 50D for a while longer and start converting your lens kit to FF capable lenses a bit at a time. There are a number of possibilities, depending upon your needs.
Either way, lenses will give you more bang for your buck, than a new camera.
If you do decide to go to a 7D, well it's nearly always a "fool's game" to wait for new models of lenses or cameras to come out. There's just no predicting it. Just within the past few months Canon released a major firmware upgrade for the 7D. I doubt they would have done that if they had a replacement model just around the corner.