My question is: do you really think it would help? If people are using
simple anonymous proxy), what are the chances they're going to have it
configured appropriately to reduce the bandwidth they use?
I don't want to weigh in on the more substantive issues here, but I do think that this specific question can be answered without too much difficulty.
For those who require a lower level of anonymity than that which Tor provides, but choose to use Tor anyway, Tor's poor performance is probably a major complaint. If they had the opportunity to change a setting from 'high security' to `one-hop proxy', and got better performance from the latter, I think that many of this group would change that setting. This would make Tor more useful to them, and decrease the network load per person in this group.
This is not to say that more use wouldn't immediately crop up to fill this gap, nor that more `one hop' users wouldn't start using Tor likewise. I don't want to say whether building one-hop functionality is a good idea, but I certainly think that some people would use it.