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I guess the answer really depends on what sort of wildlife you want to photograph.
I have the FZ18, the forerunner of the FZ28. I don't have a Macro lens (I don't photograph many insects, and am happy with the standard macro feature for flower shots), but I did buy an Olymus TCON 1.7 converter (rather than the Panasonic one, mainly because the latter was virtually impossible to get hold of at the time). I use the 1.7 converter whenever I go out photographing birds (in the garden or at reserves) and am pleased with the results I get (but I'm only a beginner, I know nothing about the technical aspects of photography).
Here's a recent example of a photo using the 1.7 convertor, taken in the garden:
