Joomla has many different tags at the moment, but no tag synonyms. Questions tagged with joomla1.6, joomla1.7 and joomla2.5 for example could all go under the same tag, as they belong to the same Joomla series. E.g. questions tagged with only joomla1.7 don't have enough visibility at the moment, even though people interested in joomla2.5 could easily answer it, it's really the same Joomla edition.
Then again we have global Joomla tag, which most questions have, and most people see.
One suggestion is that we have one tag per Joomla series (for example, 3.0, 3.1, 3.2 and 3.5 would be synonyms), so we don't dilute questions which are in the same scope (sorry for the poor phrasing).
Another suggestion is to make everything related to Joomla synonym with joomla, so that all questions would have high visibility. People who answer Joomla questions are anyway likely to answer question for any release version. wordpress is not broken into many tags per version, and I think it's a good thing