I guess my question back to you here is - for what reason are you thinking about top dressing? I'd worry a bit about the compost adding unwanted, unneeded nutes - particularly nitrogen... but worm castings, on the other hand, is something that is impossible to over-do - i.e., you're not going to harm your plant and will probably help a lot... So I'd vote for just the worm castings but give the compost a miss...
Good luck!