as far as i can tell, stories about better search results and particularly faster download speeds as an ultrapeer are a myth that comes from the assumption that 'if youre connected to more hosts, you have more places to download from/search from'. this is not the case, as your queries are being forwarded beyond the hosts you're immediately connected to.

also, as an ultrapeer portions of your bandwidth are being used for communication with all these extra hosts youre connected to, like, forwarding their queries from one to another etc, all bandwidth that you could use for uploads/downloads if your were running as a leaf.

bottom line:

-there are plenty of ultrapeers out there
-it wont improve your sharing experience

so there's no need to worry about being an ultrapeer or not.