Of late I\'m facing the issues that points finger to VC6 compiler.
Few of them are:
General rule seems to be that a new version is an upgrade and is thus worthwhile.
However! you have to pick the right time for it, there are so many bugs fixed, but you then need to be aware of the new bugs and variations from the standard.
Set aside time for the upgrade. Upgrading compiler versions could well be a project in its own right, make sure you have stable code and good tests before you do an upgrade and when you finish prove that it is still working the same.
You may be forced to upgrade when you start to develop for Vista as VC6 doesn't provide for code signing easily and the redist is not in a form that Vista likes. (want at least VC2K5)