I think it would be worth it if you plan on selling it. As far as I know, the cost for VGA grading is around $75 but the added price difference in selling is hundreds.
I'll slap a sticker on a plastic box for half that price if you like!
Three things to remember -
1) By definition, VGA haven't verified the contents of a sealed game. There's no guarantee there's anything inside (unlikely, but I have opened factory sealed games with missing contents before). You're paying for a good looking outer box, nothing more.
2) The plastic used to seal games (not the VGA box, just the actual seal) isn't preservation grade. It's only designed to keep them clean and untampered with during transit to a store.
3) I really don't understand why people care so much about what these people think that they want to pay them money to give your game a number. Has anyone really scrutinised their system? Can someone tell me the difference between an 85 and an 86 graded game?