I'd like to add at this point that my birds LOVE their mirrors! I've thought about your post and can't think of anything mean about it!
Birds love mirrors. They fall in love with them. They kiss them, feed them, talk to them, sing to them. At first I only had one keet, and he just danced with joy when I put it in his cage. Now I have four keeties, and they still love their mirrors. Also they don't like me to move them. (the mirrors!) Silly little birdies.
The only reason I can think of , NOT to get a mirror, is if you plan on extensive training. and also, you might wait till you and birdie bond. But my first was a rescue, and he bonded with me immediately, and always thinks he's the only one I should talk to! I got the mirror because I work, and wanted him to have company while I was away. I didn't get another bird at first because I wanted him to get healthy first, since he'd been out in the world and had health issues.
Not mean. Do your little birdie a favor and get him/her a mirror, whether you get more birds or not! lol