Bill, having used Mach for several years, I find the best approach is to only upgrade when either there is a new feature you absolutely need to have or there has been a bug fix that is important to you.
Unfortunately given the tight programming resources, Mach isn't tested that thoughrowly (sp) when new releases are created, so sometimes a new release will come along with an unexpected bug or 2.
I would look at the release notes link next to the download link though to see if between .020 and .029 there were any bug fixes you needed. I'm currently at 0.026 because I needed a subroutine bug that was fixed.
Good luck-
Paul T.