Melvyn,
Not a lot of time to answer, but here are a few thoughts, some of which Andy touches on.....
Carts allow courses that wouldn't have otherwise been possible in the mountains. They also allow them to be stretched further through real estate (not quite as nice)
Even "walking holes" need to stretch the distance between green and next tee to accomodate paths safely in those areas, so courses are a bit bigger and not as walkable almost by definition. In some cases, such as real estate or to use great topo, holes have been separated by far greater distances. Travel time between holes is a signifigant portion of slow play.
Whereas we used to worry about walking circulation, i.e. the approach area and the direct walking line to the next tee, we must now worry as much or more about the walking circulation from cart path to green. On expected high play courses, bunkering can be affected to make sure it doesn't block that circulation. Granted, that could also happen on walking courses, but more the front and back bunkers, whereas cart circulation requires us to consider the side bunkers more often. Ditto on the fw bunkers, with fewer being placed on the cart path side of the fw if encouraging cart circulation is desired.
At first blush, I think carts wouldn't impact speed of play any more than walking, circulation wise. They just impact it differently. Most blocages are probably linked to routing, i.e., if golfers must walk back to the next tee from a green, the next group must wait if they are walking or if they are going to their carts. I do see a lot of scorekeeping in carts before moving, but that always happened walking as well.
Most gca's also devote some earthmoving to hiding paths, which can lead to more drainage structures as well, if the path is tipped against the view line artifically. Some, like fazio go to extremes to hide them - IMHO they are so far out in the rough that they add travel time to the round, if used at all! Even at greens and tees, paths can be placed too close or too far from those entities. If too far, people take short cuts. If too close, they visually impact play far too much.