I think that most of us don't come anywhere near using the potential in our cameras, and that honing skills and craft is a much better investment than buying new gear
My first digital SLR was the Minolta 7D. This camera was a first generation digital camera and came nowhere near what today's cameras can do. It was a 6 megapixel camera with a CCD sensor that struggled pretty hard already at 400 ISO and was in agony at 1600.
Still I managed to get some really decent shots from this baby, which I actually loved and thoroughly enjoyed using, but abandoned soon after I bought it because I changed to Nikon. I shot about 15,000 frames with the 7D and going through them in Lightroom today, I'm sometimes surprised over the quality, which didn't impress me much back then.
The Nikon D200, which I bought soon after was a far better camera. The resolution was 10 megapixels, which was already an improvement, and the specs said up to 1600 ISO boostable to 3200, and at 400 and 800 ISO the Nikon did actually deliver nice images while 1600 was pretty noisy even though the noise was “nice” and could be reduced.
I bought a Nikon D40 as a backup for the D200 before going on a US trip, and this little camera really had a lot more potential than its modest appearance and specs promised. This unimpressive 6 megapixel body in combination with the Sigma 10-20mm in particular, has shot me a lot of great images and earned me back its low price many times over. Most people would not think that a camera such as the D40 could be used for anything serious not to mention professional, but I have sold several magazine and book images shot with this camera. Treated right, equipped with a good lens and exposed and post processed right, its 6 megapixels could easily suffice for a full magazine page.
It had a lot of potential.
Like many others, I have upgraded my cameras several times since I started taking pictures, and even though could still shoot with the Minolta SR-7 film camera I started out with (had it not broken down beyond repair), I'm a gearhead, and I like upgrading my cameras and lenses. And I ventured into digital as an early adopter. Since then the development of the cameras and sensors has been substantial, and I have tried to keep up by buying a new body every now and then.
But even though I started out early using digital, I have become a what I have always referred to as a “third mover”, buying not the newest, and not even last year's model, but the model that everybody else is selling. Proven and mature technology has some huge advantages, and I have lagged behind in most of my gear investment due to this philosophy.
My own motivation for buying new gear is part the irrational longing for something new and better and part an objective need for or wish to have certain facilities or qualities that I didn't have before.
I bought the D200 to skip Minolta and get into a more widespread and better supported brand.
I bought the D40 as a backup body before a long journey.
I bought the D300s to improve image quality and get a more modern body with a better sensor, a better LCD and better facilities.
I bought a D5100 to get HD video and the flip-out LCD screen.
I bought a D700 because it was a darned cheap way for me to get a full frame body.
I have been casting sideway glances at the new D500, which definitely has a lot of potential - a lot!
I have at the same time been eating my way through Point&Shoots, and have shot a lot of really excellent pictures with those. None of these acquisitions has made me a better photographer, and apart from the physical factors of the full frame sensor, I can get equally good images with the old D200 and the D700. There will be situations where the D700 can perform and the D200 will lag behind, but in good conditions, there's surprisingly little difference between the 10 megapixel D200 images and the 12 megapixel images from the D700.
If someone told me that I'd have to shoot with the D200 for the next year, I would not be deterred. It's an excellent camera, and it still has a lot of potential.
But I'm a compulsive upgrader like most other people I know, and in that respect I will probably never fully utilize the potential in my cameras - past, present or future.