What would be considered a healthy rate of traffic will vary from industry to industry. I operate in a very small part of the commercial finance field and my site is either first or second on all of the major search engines but generates a comparatively small amount of traffic compared to more popular search terms.
The
overture keyword tool will give you some idea of the number of searches for each search term.
I see that 226 people searched for "mezzanine finance" in July whilst 562,515 proved that the word "sex" was a somewhat more popular search term