Yes. Many people (myself included) believe that not having boost increases chances of rare dragons. I tried many times to get my first rainbow, to no avail. Sold all my boosts, got it second try. Since then I have had no boosts at all, and you can ask anyone here, I'm usually the first on the forum with new dragons the day they're released. New dragons are EXTREMELY easy for me to get. I'm not saying all your rares will pop up after you sell your boosts, but it might help.
Hell, for all I know, it might not even help, but like the gene theory, it appears to help, which is good enough for me!