While a certification may help to establish your skills and knowledge in areas outside those in which you've worked in the past, it won't make any difference if you keep working in your areas of core knowledge and competence. The same is true for a degree. But since mainframe related work is scarce these days I'd urge you to exploit every conceivable contact (former coworkers, bosses, friends, family, and so forth) to try to find such work -- you may be right on the money in seeking some tangible evidence that you're able to retool and have developed additional marketable skills.
Depending on what you want to do, a degree may be more or less relevant. But for most technical areas where certifications are available (you mention wireless and the CWNP program) entry-level credentials alone aren't enough to find work, either. Thus if you do want to retool you may want to plan for an extended campaign in which a series of temporary or volunteer jobs may combine with cert training (and college level courses, whether or not they lead to a degree) to help you make the transition from mainframe maven to whatever it is you decide to do next.
I applaud your thinking, and suggest you pick an area that really captures your interest, but also offers work opportunities (wireless technologies,
information security, and Open Source/Linux are all good areas with great work potential). Start working on some schooling and possible certification. If you want to pose me some more specific questions once you've settled on a couple or three target areas, feel free to post again.
This was first published in November 2003