My wall-to-wall carpeting must be 25 to 30 years old, and we are not in a financial position to replace it, either. We have almost always kept a carpet shampooer, and have had good results with our current Bissell.
At one point, when DH and I were both working, we looked into getting hardwood floors throughout the house. We would have bought a few area rugs, too. But then our money needed to be spent on gutting and re-doing our bathroom, so the old ratty carpets have remained. Then, we had two extra kids and decided that hardwood floors might be a bit hard if they fell on their heads. (Our kids all have big heads, so that happens more often than you might expect--they're all top heavy, LOL! Seriously, our 18-month old is in the 34th %ile for height, 15th %ile for weight, but his head is in the 84th %ile.)
So we will probably keep our old carpets until we sell our house. Either we'll replace them with hardwood floors (the kids will be older then, and hopefully more coordinated), or give the buyers a flooring allowance when we sell. Until then, we'll just shampoo the carpets when we're expecting company!