Hi E.J. I'll try to answer a few of your questions. First off.. I have a 20D and shoot wakeboarding, basketball, soccer, and various buildings, portraits, etc. The amount of post processing you do depends on a few things... first... the shooting situation. If it is a hazy day, a little levels adjustment will really make your photo pop by making the black true black and the white true white. Saturation adjustment can make it pop as well. Second is how closely you nail the exposure. If you underexpose a picture, you'll need to use levels to bring the exposure up, same with overexposing. Third is the quality of file you shoot. The 20D will shoot various quality levels of JPEGs and it will shoot RAW. RAW files take more post processing because they aren't processed in the camera and compressed the way JPEGs are.
The whole truth is that digital has all but done away with the old ways of photography. Getting a really good picture doesn't take a lot of work anymore, many people just snap, while paying no attention to settings, then fix it up in the post processing. What did photographers do 20 years ago when there were no digitals? The SLRs we have now are on the same level as those cameras.
The difference in point and shoot versus DSLR isn't just about image quality. I have seen LOTS of awesome pictures taken with a point and shoot. What a DSLR gives you is the wider range of focal lengths (with a wide range of lenses), faster focus, less shutter lag, higher ISO capabilities, more custom functions, and larger file sizes among many other things.
Only you know if a DSLR is going to help you out. Can you live with the pictures your Sony gives you? Do you feel limited by that camera? Why drop big money on a new camera if you are satisfied with what you have? Hopefully you wouldn't be looking at a DSLR if you were happy with your camera, cause that would mean you have some major camera envy...
Let me guess... you are shooting auto mode on your point and shoot in an indoor hockey rink and getting blurry images. Know why? The aperature and ISO on your Sony aren't flexible enough to give you a really good low light performance. The camera is doing the best it can, but it has to drop the shutter speed considerably to not underexpose the image terribly. Want to know something else? You are going to get similar results with the 17-85 lens. I guess you want to know why... When you are in situations that are "stressfull" for the camera... meaning low light or extreme high contrast situations... don't shoot auto. As great as auto is for general shooting, it can't do everything. If you are in a low light situation you are going to have to crank the ISO up and the aperature number down to get a shutter speed that will freeze action. Now back to the lens... the 17-85 lens is a f4-f5.6 aperature lens which means the aperature is f4 at 17mm and goes up to f5.6 at 85mm. The MOST I stop my lens down for low light is f4, and that is only because I use an extender for soccer and it makes my largest aperature f4. Even then I have to use ISO 1600 or 3200 and clean it up with post processing.. which you don't want to do.
Oh yeah.. just in case you don't know.. lower aperature number = more light being allowed into the lens. Higher ISO number = more light being allowed into the lens by simulating a "faster" film = more noise. Stop down means closing down the aperature, which means a higher f number. Confusing I know.
Back to the lens... shooting at 17mm f4 you MAY be able to squeek by if you shoot ISO 3200 in a well lit arena. At 85mm f5.6 you have little chance of getting a properly exposed, sharp picture without using flash. Now you can use flash, but in my experience the popup flash on the camera either isn't strong enough to reach your subject, or it creates nasty shadows and a fake look.
Ok... I think I need to go back a few steps... shooting sports like hockey and wakeboarding you want the highest shutter speed possible to freeze the action. The reason you are getting blurry pictures is that your Sony isn't able to situate it's settings such that you can get a shutter speed high enough to freeze the action. For me with soccer and basketball 1/320 is the minimum I'll shoot, even then things like moving arms or running feet will be a little bit blurred. You really want to be 1/500 or faster.
Whoa... I got REALLY carried away.. sorry about that.. probably nice and confused now. I'll try to sum it up quickly. Yes, with the correct lens you will get significantly more keepers than you are getting now. The 17-85 probably won't do that for you with hockey, and it will be pushing it with wakeboarding because you really need more focal length. The 17-85 is a great walk around lens.. meaning if you were shooting flowers, sunsets, landscape shots or general "around the house" type stuff, it works great. For sports like hockey you need a good low light lens, for sports like wakeboarding you need more length.
Now for the fun part... my suggestion. The 20D is a VERY capable camera. There are guys making good money at photography using the 20D. I don't have experience with the Nikon line, so don't know about them. The Rebel XT is also a very capable camera, very similar to the 20D. Why did I go with a 20D instead of the XT? Glad you asked... I wanted 8 frames per second as opposed to 3, cleaner high ISO, faster focus, and of course being able to say... "yeah, I have a 20D." Ok, little camera envy there...
What I listed above are pretty well the only major differences between the XT and 20D, if you can live with that... go for the XT, if you really want that AF performance, frame rate and high ISO capability, then the 20D is the way to go. Now.. for a lens. I know the 20D comes in a nice neat little package with the 17-85, but are you really married to that lens? If you are really wanting to get some good shots look into just dropping the cash on a 70-200 f2.8. Yes, they are about a grand used, but that is the go to lens for many, many professional shooters. It will work great in the hockey arena, then you can step right onto the boat and have the perfect lens for wakeboarding. It is fast and tack sharp. I use mine at least three times as much as any other lens I use.
Well... now that I have confused, annoyed and downright bored you to death I'll shut up. Feel free to shoot me an email if you have questions.. I'll try to answer them more efficiently next time.