This has been discussed on the mailing list and reported (MVERSIONS-131) with the conclusion that this would best be handled through implementing support for wildcards:
mvn versions:set -DgroupId='*' -DartifactId='*' -DoldVersion='*' -DnewVersion=1.2-SNAPSHOT
This improvement is reported as MVERSIONS-228; it doesn't appear to be implemented in the current (2.1) release of versions-maven-plugin
.