To possibly widen my choices of toys to modify to PC control, what do you think about ease and complexity level on just making any toy vehicle and adding some bits and turning it into a PC controlled robot?

I know if it is just a paperclip like axle, with no steering mechanism I could probably only make it go forward and backward by hooking up a single servo and a gear to the axle. That might be all the action I need for that particular vehicle though. If I can get multiple toys moving around with sensor cues to have the toys pass work off to each other maybe I can get some productivity out of it. Maybe the whole set does nothing but dig in a hole and then work the dirt out of the hole and drops it off a ramp into container already on a dolly, slow yeah, but I'd rather have it do it slow, all day, than for me do it.
But what about appendage action? Just attach some servos and springs? Record servo position and test the playback and just call that action to the appendage whenever it is needed?
What do you think, how would you go at it?
fun fun fun