Your question about whether certification is necessary or not for somebody with 20 years of IT experience is right on the money. Unless you want to work as a technical expert, certification isn't really necessary for somebody with your years of experience and knowledge base.
Unless you want to leave management and return to work as an individual technical contributor or expert, it's probably not necessary. OTOH, if all the jobs you're interested in require certs, then perhaps you will want to pursue those that are in greatest demand in your chosen companies or organizations.
That said, most managers don't maintain technical currency, and find that business training or skills are more valuable. Thus, for somebody in your position and career status, I'd urge you to consider an MBA or an engineering master's degree rather than a certification.
HTH, and good luck!
This was first published in September 2002