Alright, for the pants, it all depends on you and what sort of fabric you’re using. I’m sure you’ve seen fabric glue before where the glue seeps through the fabric and you can tell where you’ve glued. You don’t want that. I would take a scrap sheet of your grey fabric and glue it to something to see if it has that effect. If it looks fine and you can’t tell where you’ve glued (and it stays on well) go ahead and do that.
Keep in mind though, the fabric glue won’t be as sturdy as sewing them on. One wrong scrape or catch on something and you lose a grey spot, leaving glue residue behind in it’s place. Sewing may be a better way to go if you run/sit/move around a lot at conventions.
And I always say go with a wig. Always. At the end of the day it’s your choice, but if you’re asking my opinion, I say wig.