Also, I am not an expert by any means, just a hobbyist. And discussions like this are far from a waste of time.
MTT's have a solid collector base pretty much everywhere but like many old crown-size coins that collector base is ageing due to limited supply, constant demand, and rising values; look at pillar-type 8 reales, or German States city view thalers / Bavarian Madonna thalers, and here in the US you are looking at $300 minimum to find a coin you'd actually be pleased to own without being scared of counterfeits and doctoring, and that's a low-ball estimate. The same thing is happening in the market for American early coppers, where rising values have made entry into the market difficult for many new collectors and competition for scarce varieties results in bidding wars with some regularity.
New collectors for old series with long histories (non-Roman/Greek ancients, medieval issues, thalers, or reales) are often frustrated with the lack of modern books and online information, or the cost of entry when such materials are available. Generally speaking, the more narrow the focus of the collector, the more expensive the books and the more obscure the information.
In addition, MTT's have been a collector interest for a long time, and there may simply not be much new information left to discover or research that hasn't already been put to print somewhere. The authoritative books for American Large Cents (Sheldon & Newcomb) are decades old, and even more "modern" research into die states and varieties (1990s) still refer heavily back to those two sources.
If you love MTT's and want to make a go at having them as your collecting interest (and it sounds like you already have many of the primary references!) then your best bet is to get in touch with the people who do the research and write the books. I think you will find that most of them will be happy to be able to discuss their passion and share it with you, and you can gain a lot of knowledge in return -- just because there hasn't been new PUBLISHED research doesn't mean that no research was done; merely that it may not be worth the expense to publish it mass-market, but it can be available if you ask for it.
edit: I forgot to mention -- 1780-dated MTT restrikes have been made nearly continuously for 238 years and continue to be made. Even though the basic design has not changed radically in that period, the engravers and die-cutters have, which creates a constant source of "new" varieties, unlike, say, Liberty Cap large cents, which have not been struck since 1795 after being first struck in 1793.