It's not the body. And the problems the body has aren't ones that the 40D will necessarily solve.
My 2 cents.
Get a x0D series for the better construction, better viewfinder, better ergonomics and better control.
If you are otherwise happy with your T1i then here's a couple of things to try first.
1: On all EOS cameras the centre AF point has the best performance. Your T1i is no exception, as it's the only cross point. Go into P Tv Av or M. Select the centre AF spot as your only active point.
2: Ai Servo has a better chance of getting the action shot that one shot AF. One Shot AF will actually prevent you taking a shot, unless the camera thinks it is in focus. This will make your moderately fast camera much slower, and the same would be true of a 40D or 7D or 1D. So go to tracking AF (Ai Servo) learn to track for a few seconds, burst burst burst, track for a few seconds, burst burst burst.
3: Consider your lenses. Dark non-constant max aperture lenses are going to really hinder your AF system. The centre AF spot becomes even more sensitive with lenses brighter than f2.8. Spend some money on a bright USM lens. The 50mm f1.4 USM or 85mm f1.8 USM will let in loads of light and really boost your AF performance. And if your AF is fast, your frame rate is up! You'll get the benefit no matter your shooting aperture. If you put slow lenses on any body, you are going to struggle. If you are shooting action, you should be using fast lenses regardless of the body.
4: Consider your format. Where are these pictures going to end up? Are they going to be A2 posters? Or 9x6 prints? Do you really need to shoot RAW? JPEGs, particularly smaller JPEGs without in camera effects, will get the most out of your cameras buffer depth. RAW is a killer, and max resolution is often overkill.
5: Memory card speed. When your 500D came out memory cards were much more expensive. Treat yourself to a class 10 card, if you haven't got one already. This won't make your camera physically faster, but it will reduce buffer bottlenecks when you are piling on the frames.
So yes, there are reasons to buy a better body, but I don't think a 40D is the answer to your problems.
Brighter glass will probably be more effective, as will a look at your technique and settings.
I used a 400D for a few years and it was a different camera with bright glass on it. Centre spot AF. Ai Servo mode. Bright USM glass, faster card. Exactly the same advice I would give to a 40D user.