Maria Theresia Talers 1741 - 1780

That's unusual and rather interesting. I looked at a few of Hall mint 1749-1769 Thalers which have various shapes on the middle bar of the E, ranging from a sort of "spade" shape on a 1749 to a backwards arrow (upside-down triangle) shape on a 1762, but have not seen one with such sharply defined forward "arrow" appearance. Based on the rest of the lettering, several letters have been recut; that along with the concavity and the flat fields suggests to me that this was a very worn-out obverse die which was re-engraved and recut to continue in service. Whomever did the recutting on the letters probably used a bit of "artistic licence" on the middle bar of the E or couldn't be bothered approximating the "spade" shape more closely.

Thalers were the standard silver unit of trade in the 18th c. for Austria and Germany along with gold guldens/florins and ducats.

As a result, the weight was standardized and tightly controlled, amazingly so considering the age in which they were being struck. Size varied depending on planchet -- some series (the Madonna Konventionsthaler of Bavaria from 1760-1780s come to mind) varied as much as 3mm in diameter coin-to-coin (40-43mm) but the weight was unfailingly very close to 27.92g and the fineness was set at 0.833. Not so much for the design -- thanks to shorter die life, some estimates say that for the 1780-SF saltire MTT's over 40 die pairings exist.

The Austrian Speciesthaler MTT's of 1746-1765 are almost universally 40 mm and 28.82g at 0.875 fineness. Coins that were overweight were adjusted via file marks. Underweight coins by more than a couple of tenths of a gram were melted and restruck. Not only did this inspire a great deal of confidence in the intrinsic metal value of the Thaler, it greatly discouraged thieves since clipping, base metal plugging, edge filing and such were easily detected, especially when combined with edge lettering.

The one you posted (1780) assuming it's a brooch without pearls looks like an issue from Günzburg based on the 5 pearl shield, crown, and long feathers. cf. Hafner 25-32 and Leypold nrs. 1 & 5 and see if you can find an exact match. It's an AUST DUX reverse which also helps narrow the field.

Forgot ...

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.