The plateauing argument is a dangerous one for me. I play several characters, my main is Sim, my second is Blanka, and I dabble in Honda and Cammy. I have been playing for years… And it is sad to say I have clocked tens of thousands of matches, and I am still improving.
There are two discussion points I think that should be covered:
I am not trying to flame but feel the plateau argument is BS.
I am not going to let you get away with that! 
Ppl make this statement out of the frustration of losing. If you?re losing to the same strategies, or finding you advancement halting, you may be looking SF from the wrong POV. Unless you win EVERY match there is always something that can always be improved upon.
Your improvement will always stagnate when you become complacent or accept the fact that you are not getting any better. I see many players losing site of the fact that as we get better at anything, there is a diminishing return in improvement per unit of time invested. Meaning if you want to improve, you?re going to need to infest more and more time.
Think of it as racing. To get a car to go 120 MPH, it doesn’t money or technology. To get a car to go 150, a basic stock model will not cut it, but small investment (money) in upgrades (technology) and a car can just hit that goal. To get a car to hit 185MP takes a huge invest of capital to piece together all the racing and custom parts needed to build/alter a vehicle to achieve those speeds. To get a vehicle to hit 200mph normally takes millions of dollars from a corporate sponsor, a team of technicians, crew, and well experienced driver. And that is ONLY to go 25% faster that a 268 HP Toyota Camry V6 sport, which you can buy for 30K.
I guess my point here is that once you?re good player, greater improvements will take much more time.
Now some players have already invested much time in the past, that very little investment is need now to improve b/c they can already beat 99% of the competition. But, many of these player are extra ordinary in some raw talent level, and have invested the time need to get better. (Choi, Valle, Wong, Cole, etc)
So hang in there. :tup: The improvement will come.
Secondly, I see player stagnation come from just playing the game and not the opponent. There is this GREAT poker commercial on TV for FullTiltPoker.com. Go here http://www.fulltiltpoker.com/commercials.php and watch the commercial by Howard Lederer: "I don?t need to see your cards." Watch it before reading on…This commercial captures exactly what I am trying to say. I bet you are still playing the game. You are thinking much more about what you are going to do, and which character the opponent has picked rather than thinking about the opponent themselves.
Decoy talked about this in his post. And Allex Valle talked about this in a Nohoho blog post. At some point you stop learning about how to play ST, and you start to learn how to play your opponent. You can never plateau on that topic.
In a set, I lose more frequently during the first round or match, to some random ass person doing the most inane BS. However, one I figure out the type of player that person is and how “THEY” play SF. I beat them many more times than they beat me. That is why you see good players go back and forth. They are constantly changing and adapting to each other. It is a dance, where the little movement of momentum change by an opponent, is almost instantaneously adapted too.
I think if you learn to play a player, you’ll see you game continually improve. Just like in weight training. Your body adapts to new stresses forced on it faster than the same old routines. Learn to continually introduce new stresses to your game that force you to learn and adapt to a variety of player types. Then I think you find the whole endeavor me bit more rewarding.
Anyway, I am not sure this help. But, it?s my 2 cents. Thanks for listening to my rant.
~fatboy