I find your logic here to be rather weird. Is "does this use power" the SINGLE factor in ALL of your decisions? And would you expect a vehicle to work without power? How would that make sense? At least with conveyors, it's possible that they might be driven by whatever machine(s) they're plugged into.
Trucks definitely have their uses. First off, I find planning, building, and tweaking a road network to be a lot more fun than just running another 6 kilometers of belts between two locations. I want my factory to look like an actual industrial base, not just a giant spiderweb of conveyors. That means roads, entries, loading & unloading stations, fences, walls, the whole works.
Secondly, trucks are a great way to move lots of resources a small to medium distance. I'm currently working with Mk3 belts, and a single truck can drive five minutes to one of my steel plants, load, drive five minutes back, and its truck station will still be spitting out the last load it brought. Since it's using Mk3 belts to empty the station, that means the truck is moving well over 270 items/minute into my base.
Yeah, you don't want to use them to drive clear across the map (that's what trains are for), and they still need a lot of tweaking (especially their AI), but they offer flexibility and an alternative to just stockpiling containers full of belt materials for every time you want to connect a new resource provider to your base. By the time I got trucks unlocked, I was more than ready for an alternative to yet-another-belt.