Ayy not a bad idea at all. +1
But I think a rank-up is a bit too much, unless it's a Cit to a VIP. No more than that.
For a free meebles gift, I think the gifts should go like this:
Cit - 100k Meebles
VIP - 150K Meebles
Exclusive - 250K Meebles
Elite - 500k Meebles
Supreme - 750k meebles
Ultimate - 1M Meebles
Special Notes? A fly one is too high. Maybe a feed note or any other one would do, but it would be randomized. Ultimately, the birthday gift should be randomized, so that it's just not stuck to one thing. It would be a rank-up, a meebles prize, or a note. End of story. There should be a key listing the percentage that a certain prize would have, so that it'd be like a slot except you're not paying anything and you can only use it once a year. That way, the one with the smallest percentage of happening is something people can look forward to, in hopes that they'll get it.