I wouldn't consider open sourcing it a net negative at all. You will get it out there, and as more "advanced" users start to use it and sing its praises, you will have more than enough to keep yourself busy helping out those who are too pressed for time or just have money to burn, or just can't figure it out on their own.
By not releasing it open source, you will have a much harder time branding yourself as a "proven" performance expert.
Compare these two "resumes":
"Original author and lead developer of the PerfPlus open source project, used by thousands of developers worldwide to benchmark and improve their applications."
vs.
"I'm a new college graduate with a few references and a custom tool I wrote that's worked well in a handful of cases."
I can tell you which one I'd be more willing to hire (if I had money :-)