I'm a bit shocked in general that it hasn't been done (at least struts with the proper lowering strut rod/shaft resizing), but I don't think they'd sell anywhere near 10k kits. The class plays a lot bigger role then you're giving credit for. Certainly more so than the purely numbers statistics.
With the 3000GT/Stealth, you're talking about a performance car. Most people who owned one when they were newer, or now, are enthusiasts, not to mention when they were newer, you had to have some money to own, let alone play with one. Even now, comparatively speaking to cars from the same years, they're a bit pricey. Given all that, owners of those vehicles splurging on performance parts was a lot more feasible, thus worth it to companies to produce parts for.
By comparison, whether people in the community like to admit it or not, the w-bodies are daily driven family grocery-getters and commuters that a handful of people (by comparison to the total number produced) are nutty enough to try to squeeze some performance out of. When they were newer, very few of those in the targeted demographic with enough income to buy one were interested in modifying the suspension. Now that they're old enough to be dirt cheap/worthless retail value-wise, they're in the hands of a few people who want to turn them into performance cars, but that also means they're mostly in the hands of people who can't afford a $600+ suspension kit.
I still think they'd sell a decent amount, so I'm still surprised it was never done, but 10k is not realistic to me.
