I like the roads, personally. I ride them sometimes on a small motor scooter or bicycle to look at the pretty scenery and places people have built, or to find places like shops or public buildings I might never have thought to search for. It's relaxing, if you use a vehicle slow enough to allow things to rez as you go along. There really is a lot that's worth seeing, some of it quite spectacular.
The unmanned tanks rolling down the road are kind of ridiculous, I think. The other unmanned vehicles are easy enough to avoid, they're rather slow. They usually aren't much to look at either, though. Very crude looking objects compared to most of SL. I didn't even know one *could* ride inside those. I have ridden in the little pods for "tours" a couple times. It's ok, but usually I'd rather use my own transport so I can stop at interesting places and find a good angle for a screenshot, etc.
The only time I've ever run into a *manned* vehicle on the road, it was a couple of jokers in a car that entertained themselves by trying to run me off a bridge into a river. So my perspective may be skewed a bit, but I don't tend to think of the unmanned objects as being what I'd call the problem. The unmanned ones are slow and pretty easy to avoid unless they're big like the tanks. I haven't ever seen piles of them, but I have seen them go meandering off the road and through fields or etc. They could be a more effective simulation of occasional traffic if they were up to par with what most SL people would actually drive in terms of object quality, though.