Well, yea… its quite nice, because the vehicles in the depot is always out of service… and i think you can sort what the lines should prioritize. You can set them to take cleand buses first, but also take new or large (or small) buses first. The time table system makes it needlessly complex. In Train fever there would only need a intervall timer and a preferences list.
For example one line can prefer to use one type of bus, the other line can prefer a other type… but if there is no available of the type it need, it takes a other. In this way they can prefer a newer vehicle, leaving all old one for sale.
The repair and clean system also makes it beneficial to have at least 3 vehicles at a time in the depot, and in most cases around 10… because there is no runingcost in the depot, its no problem having a fiew spare.