In my humble opinion I will quote my son.
8 years, carpet fitter & wood floor layer
he told us not to bother with steam cleaners as they only push the dirt further down in the pile, and once you start you have to keep doing it!
Trouble is they really only clean the top of the pile, any stains are best removed by a product called Vanish. For red wine stains, pour white wine over immediately, if not possible use Vanish ASAP.
I too am changing over to wood now, as it stops that dark line around the edge, which is caused not by the hoover getting close enough, but the dirt that rises from below.
Hope that helps.