I had good luck with convertible top window cleaner and I stitched both the zippers in my front soft doors back in, having gotten them cheap in that condition.
A speedy stitcher is a nice to have, but not essential. The thread used in the originals is not so heavy as the wax twine used in SS's. I used Coats and Clark Outdoor thread, which is about a v70 thickness. It is available at many WalMarts and most fabric stores. One spool will last you. While at the store grab a glover's needle, as it has a nice triangular point that I find is easier to punch through old tight stitch holes. There is no need to "resew" the zippers in, just rethread the old holes, if that makes sense. it took me 45m per zipper. It was tedious, and my fingers and eyes hurt from the strain and repetition, but I am satisfied with the job and haven't had any problems.
You'll want to have the convertible top window cleaner on hand anyway for annual cleaning of the plastic windows, so that purchase isn't unnecessary. The thread and needles will come in handy for other repairs. Taken that way, there is no reason not to try, as the materials will not be wasted over time.
Bulldogger
Bulldogger
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