It's not the gear, it's you.
Most of the time this is true, but it's not always the case. I personally needed an upgrade. The camera I am using is noisy, only useable below ISO 400, 800 at most, with a dim, small viewfinder (0.75x on APS-C!), has poor ergonomics, has only one control wheel with the aperture adjust button is too far for my thumb to reach.
I've been using this particular camera for maybe four years now. I am very familiar with how it handles and can use it pretty intuitively, which makes it's shortcomings all the more apparent. When I looked into a replacement, I was looking for something that had a bright viewfinder, two control wheels and modest low light performance all the while meeting or exceeding the IQ and dynamic range of my current camera. I knew exactly what I wanted, not just a vague idea of better equipment to improve my photography - which I have little doubt will change much once I get my a700.
If you're thinking it's a lack of equipment, you've got to ask yourself what specifically it is about the equipment that you think is lacking. If you have only a general "my camera can't do that" attitude, it's probably you, not your gear. If you have specific, measurable concerns then, yes, it's probably the gear. But in any case, any decent DSLR can produce good results. It's just not a matter of not being capable, it's a matter of how awkward or cumbersome it is to get there.