For us there's also the aspect of making a living, rather than just selling your services and photos. Making a living means staying in business for the long haul and ending up with paid-up mortgages on home and commercial property, retirement programs, insurance, days off, and in the end an intact business that you can sell rather than merely a box of worn cameras and little else.
That all takes serious business management, long term decisions, budgeting, and frankly, making sound business decisions about when and what technology to buy. If your gear is adequate to the market demands, no buying replacements in spite of what the Jones's are flashing. If yours still works and meets market demands, keep it and divert your income into retirement accounts, extra payments on mortgages, life insurance, health insurance, and lots more.
During our professional tenure (months shy of 20 years now) other photographers have come and gone. Most sell their services cheaper than we do, and frankly several were technically better photographers. But ALL went broke and got out of the business. They drove nice cars and used the latest gear, but they never built their businesses. Meanwhile, in that same environment we have paid off a commercial property, paid off the mortgage on our house, maintained investments outside the business, built up satisfactory retirement accounts and life insurance policies, and lived a normal lifestyle outside of our business including vacations and regular days off. Meanwhile our "new" car is a 1997 and we haven't bought any new camera or computer gear in 3 years. We've had some windfall income this year and we certanily need replacement gear. But it's in savings right now as a contingency fund and the decision to buy replacement gear won't be made till the last minute in 2008, and will be weighed against other expenditures.
I'll go back to our mantra: A photography business is 95% business and 5% photography. If you don't eventually make a living at it and survive for a long career, how professional is that?