I've said it before, but it's what I believe - any CC'er who gets busy enough will end up with a TM.
Nearly all the people who do get TM's have worked their way up from porties, and wouldn't want to go back.
TM's do do a better job - if not in the cleaning, then in the drying - I was amazed at how dry we were leaving carpets when we first got a TM.
It is easy & obvious to charge just that little bit more, or convert a better percentage of quotes, when you tell people you've got a machine 7x or 10x times as powerful as the bloke down the road with "One of those little electric machines." (and it's self contained, hot water right from the start, etc, etc - it is a very easy sale for us if we're quoting against a porty user.)
We're all allowed to talk b******s on our website, but the link from Steve, presumably Ian's site, does seem to hit a high in this regard - we TM'ers are "creaking (sic) nuts", apparently.
Running costs are negligible compared to greater output. If you really want to spend time engaging with customers, you could get a helper, which allows that and more throughput, but my betting is that the answer is in my first sentence - you say you don't want a TM because you're not busy enough.