As a very general rule of thumb I work on the following order of importance: Note I'm only going to talk about technical details, skills are a separate factor.
1) Lenses
2) Lighting
3) Camera
That does not mean the camera body is worthless, it just means that I am far more likely to spend money on good glass and good lighting gear before I invest in a camera body. This is the typical pattern for most people and generally represents the greatest gains that you'll get.
Lenses - these are what directly control your light that you work with, further they also control what and how you can shoot. You want to take wideangle shots you need a wideangle lens; you want to do macro you need a macro lens; etc..... There are, of course, workarounds for many situations, but at the end of the day the right lens for the right job is important and will generally be the best way to get the best result.
Furthermore lens technology advances at a much slower pace and the gains lens to lens can often (though not always) be more marginal. This means your lens investments, when spend on good quality glass, will keep their value and use for a much greater period of time. 10 years - 20 years maybe more.
2) Lighting - well photography is all about light, so be it just a reflector or a full studio setup; equipment that allows you to exert indirect or direct control over the lighting really makes a massive difference in the quality you can get. In some fields its even more essential than the lenses (eg product shots are almost all about the lighting setup). And again this tech advances very slowly, probably even slower than lenses when you are using manual flash power outputs and not auto tech - so again its solid investments in gear that will last and retain its quality for a long period of time.
3) Bodies - the thing that records the light from the lens itself. From the current new market there really are no bad choices here, from rebels up to 1D bodies they are all solid choices; if used correctly of course. Now I'm not saying that a rebel is as good as a 1D, not at all, but what I am saying is that the quality gain is more minimal when comparing the two than if you compare a bottom market lens to a top market one.
In addition the greater gain in bodies isn't so much the quality, but the additional features; the focusing accuracy and speed (though of course tied and limited to the lens speed there); the ISO range and quality of it; the metering; etc....
However much of this tech advances faster, so whilst older bodies are still working, they are not as easily comparable to the modern offerings.
In the end that is my way of thinking; I'm far more likely to put down £4K or more on a single lens long long before I'd put down that money on a body. That isn't to say that the body is worthless, its just less important in my way of thinking to the final product. I've some justification for that too - I've a 400D and a 7D and to be honest I'm happy enough to use whichever body is closer to me at the time to get a shot. Sure if I want to head out to do wildlife the 7D is far preferred for its AF functionality and greater usable ISO range; but I could just as easily take out the 400D if I were not shooting in especially challenging lighting.
Now glass wise I've a 70-200mm f2.8 and a 70-300mm sigma (cheap one) - I've not touched the latter since getting the former and honestly I wouldn't be happy to use the latter now that I've got and used the former. The quality difference in the field is massive - both in optical quality, but also in AF performance.
However I will say that the body discussion HAS to be tempered against the format you want to work with. If you want to work with a 1.6 crop camera body that's great - but if you want to work with 35mm (fullframe) then the body upgrade has to come sooner rather than later. Same for if you want to do medium format or any other size of format -- in that situation you've got the get the right body early on so that you can build you working lens and methods around that. Trying to go the other way sort of works, but can run the risk that you're getting results you don't quite want for a long time and that you'll have to change the lenses you use to ones that retain the angles of view that you've grown used to working with.