It wasn't just about the finger, the finger showed how he was powerful and can never be bested.
by moon blasting it off it made him look weak to the other Monsters and they fled from fear by Moon (and by extensions all of mewmans since Mewmans been kicking their fucking ass since they landed on their monster land)
by Moon disgracing him it brought back the Mewmans might and authority.
Toffe wanted his finger back to show the other monsters that he IS invincible and is powerful enough to topple the Mewmans rule and lead his revolution back.
hard to get once you just finish the movie but it makes sense if you think about it, he never cared for the wand. he just wanted it gone so that way he can go back to getting his army up again and start off from where he left off.