In a challenging situation like shooting indoor sports, you are getting different benefits from upgrading camera body and upgrading lens.
In terms of camera body -- A newer camera may give you better burst shooting. For example, I took Tae Kwon Do pics of my kids breaking boards, at 10 frames per second. So it was only about a 5 second event -- I just held down the shutter button, and picked the best 1-2 pictures out of 50.
Also a newer camera may have higher ISO range. Thus, you can use a high ISO to allow you to shoot at a faster speed, even with a lesser lens. But even higher ISO will only help you so much, and still degrades the quality of the image.
Next is focus speed -- This is a combination of camera body and lens. Obviously, for sports, the faster the focus, the better.
And that's where a high quality zoom lens comes in. A 70-200mm with a constant 2.8 aperture -- Lets it more light. Letting you use a faster shutter speed, at a lower ISO, then you would be able to do with a higher aperture lens.
Unfortunately, fixed aperture zoom lenses are EXPENSIVE. A high quality 70-200mm 2.8 can easily run $1500-$2500. Tamron makes one that is about $750. I have no experience with the lens, but I have read reviews online, suggesting that is has a slow focus making it less than ideal for sports. (The reviews suggest that's the compromise you are making for the much cheaper lens).
Now I have had luck shooting Tae Kwon Do with my ultra cheap zoom lens (70-210mm, 4.5-5.6). But that's from fairly close to the action, in fair indoor light. Certainly, to get the sharpest possible pictures, and to truly capture mid-air type action, a higher quality lens would be far preferable. But you *might* be able to get by with a real basic "kit" type of zoom lens.
dSLRs are truly no longer critical to get high quality results in every type of photography. I actually prefer my high grade Point & shoot for some types of shooting.
But dSLRs are still king for sports shooting.
There are some mirrorless systems that are basically dSLRs in a smaller package. Like the NEX system from Sony, which could be worth a look.
Within my limited knowledge (I certainly don't know every camera in the world), in a mirrorless-compact mold, there is the Panasonic FZ200. Constant aperture 2.8 lens, up to 200mm zoom. Shoots 12 frames per second. It *might* be able to handle sports well, though I really don't know.