I always find the "you can't do it" aspects of this forum quite helpful. Coupled with the "you must buy more tools", it must be encouraging to those without limitless funds to find their situation has been declared hopeless by the experts. Certainly, giving up is an option as well, right?
Puck - when I couldn't afford a stacker when I was starting in the trades, we used a wobbler due to its speed of cutting. And while you could get carbide tipped dado wobblers, you couldn't get carbide tipped router bits that were any good. So we were stuck with wobblers for making site built cabinets. This wasn't the problem some would make it.
Set the old wobbly up as close as you can, then use a pencil to make reference marks on the hubs (both side) and blade (both sides). Test. Open up or close as needed to get the perfect thickness you want. Granted, it takes patience, but you have a tool that works well within it means. That translates that all precision must come from you.
After you get the width cut to you satisfaction, take an awl or sharpened ramset nail and scratch into the metal your personal reference points. (BTW, the ones on the hub are accurate within about
1/8" or so, give or take 1/4", so I would use them too much!).
I have an old one in my shop that was from +/- 1975 that has scratches for 3/8", 1/2", and 3/4" plywood for shelves.
My complaint with the wobbler end product was that the same as Leon's above, that bottoms weren't really smooth and flat once you got to the wider limits of cutting capacity. However, an ultra sharp 1/2" butt chisel cleans up the cuts in seconds. However, unlike Leon, I didn't have depth cut problems; the brand of dado I used could easily be set for depth, but it cut the correct depth on the outsides of the dado leaving little tracks inside the cut itself. The difference could be different makers or models from the same makers. Leon's point addressed the only downside I saw in the field.
While I heard of wobblers going out of adjustment while in use, mine (all 3-4 of them were purchased at Sears somewhere between '75 - '80) never did. I don't think the boys tightened them properly, as in not enough.
If you want to use what you have, that tool will serve you fine with the proper setup. While it certainly isn't as elegant or as easy a solution as the $150 sets, you can get it where you want to go with some patience.
Robert