Maybe these are dumb suggestions because they are too easy, too complicated to implement or they can be done actually(I suck at programming :D) but still:
1) It would we awesome if one can make the sprites/objects don't collide/overlap with others instances of the sprite/object. Making the sprites themselves obstacles or solids doesn't work (don't know why)and while the flock idea has some nice uses it wont help if someone wants his individual rts tanks going to different places. (*)
2) This is harder probably: if the destination is unreachable why don't make the sprite/objects go to the nearest empty/reachable place instead. Something like "find nearest path to X,Y"
(*) Using "on collision" + wait 4 the further instance it gets a little better but they still overlap randomly and sometimes even trespass solids.