- How much resolution do you need? Do you really need the 18mp new camera? Yes, it may be cool to brag about, but stop and think about where and how you use your images. Do you print? Are you printing images above 8x10 or 11x14? Do you crop images or have to fix perspective a lot? Do you have a computer powerful enough and with enough space to handle the file sizes? All of these are questions you should ask yourself.
A new camera body maybe all you need. The added mega pixels and new features are sometimes enough.
On the other hand, maybe you should upgrade your lenses instead of your camera body. Are your lenses too slow? Not sharp enough? Think about how you shoot and what your limitations are with your current lenses. If you want your images to look sharper or want a shallower depth of field, you may want to upgrade to a faster 9aperture speed) lens, or to a lens with better glass (example: Nikon's ED glass or Canon's L glass).
Staying within the same brand can save you money. Hopefully you will not have to make a major switch to a completely different system. If you can simply change out one or two pieces it can save you money and give you new gear at the same time.
Consider buying used. Just because you are ready to upgrade does not mean you have to buy brand new. If you have had your camera for two or more years you might be able to upgrade to a newer model and still get it used. Also consider trading in your equipment to upgrade, instead of keeping all of the unnecessary equipment that you will probably not use again.
If you are going to upgrade your equipment, you should sell (or trade in) your current gear as soon as possible. Once new equipment models are introduced and get into the market, then the prices on the older models are going to start dropping.
Don’t upgrade too often. Take the time to do a little research on the camera, lens or accessory compared to what you currently have to see the improvements. Is the improvement in picture quality or the one or two new features worth the money?
Sometimes it's just not worth upgrading. If you feel comfortable with the camera you have and you are happy with the picture quality, keep it and use it. If you are just bored with what is in your camera bag, then consider adding some new items to your equipment collection such as a flash, filters, or other accessory.