Hundreds Of Minisheets Since 2010 From Africa (Guinea, Togo, Niger, .)

Good luck even finding wallpaper stamps available at local post offices in these countries. Some wallpaper materials do seem to get surcharged and/or overprinted periodically. But it's hard to know for sure if these are actually emergency issues. My thought has been that these are issues supplied to the country by the printer when there are shortages and a need for something very quick for the local post offices to use. In many cases, these stamps are not even priced by Scott. So they must be quite scarce for those interested in trying to find them.

There are 2 main agencies - Inter Governmental Philatelic Corp out of NY or NY, and Staperijia (spelling?) out of Europe (eastern?) who make IGPC look restrained.

Stamperija Ltd in Lithuania.

"So if I'm brave enough to travel to Togo and send a postcard home to myself using these "stamps", the postcard's value will be very high."

Only if the stamps are used in a contemporary timeline. In the US, you can buy a shoddy but complete 300b booklet pane anytime, put it on an enevelope and mail it. The stamps are still valid for postage. A full 300b on a cover is valued at over $1000. Your cover will be valued NIL, as it is provably a concoction of "the real thing".

When the country of Southern Sudan came into existence, some did "find stamps". Some are mostly Chinese "entrepreneurs" as those stamps were (and still are, I think) printed in China. And in China, when daytime ends and the supervisors have left for a good night's sleep, an hour later lights are turned back on again in the factory and machines are restarted for "the night shift productions". Shoe manufacturers like Nike, Addidas, etc in particular suffer a lot from such "night shifts". In Asia you can get "Noke" and "Addidos" shoes with almost identical quality, at a fraction of the real price.

There are business people that are/were visiting South Sudan and they take/took the chance to mail envelopes with South Sudan stamps on them (if available, at all. Many issues didn't even make it to South Sudan, particularly the myriad of value-overprinted stamps). Some letters even made it through the sytem, often taking weird routes. Such covers sell quite well.

About going to Togo:
The actions of one, or even ten collectors, do not convert wallpaper stamps into postal stamps. A stamp that was used solely for collection purposes is not a postally intended use of a stamp.
Example: You can buy mint wallpaper stamps and take them or send them inside a package to someone you know in Africa or the dune countries, and have them posted back to you with genuine cancelation. This way you will (try to) have Nude stamps from Abu Dabi. Do it with 1000 collectors regularly and it might qualify for new postal usage.
Personally, both wallpaper stamps, CTO's and mint stamps are all stamps that did not serve the prime destination of a postal purpose of having a postal item, like a letter, being transferred from point A to point B via the postal service. So if you legitimize or kosherize one of the above, you might as well accept the rest.

Apart from that the idea works only for stamps that saw postal use but are so exteremly rare they command high prices, thus making the discussion about wallpapers completely irrelevant: might OP have been joking?

If you are looking for inspiration, I recommend you check out this auction from 2.5 years ago-
https://stampauctionnetwork.com//V/v754.cfm . It covered a lot of ground.

I too am very interested in astronomy-themed stamps, starting with the US. I have been trying to get both major and minor listings and non-listed errors/essays/proofs. The minor listings are super challenging if not impossible/questionable listings. I also think there are a few folks who have the stamps I need but who refuse to negotiate blocking my completion. I believe the journey, all the interactions, and the learning to be more fun than actually completing.

Responding to a question on page one of this post. It is possible that Einstein and trains are pictured together because in explaining or trying to understand relativity, many of his thought experiments dealt with observers on trains and stationary platforms. But who knows

I have seen other issues with two unrelated topics together. They seem to think if they throw more topics together they can sell the same issue to 2 different groups

I have always had an affinity for souvenir sheets. Not the really modern ones but anything up through the 1950's. Many of them were issued in low numbers relative to their single counterparts but were also invariably targeted to collectors and not for use postal use. Their size alone mostly precludes using them in a practical manner. Because of this they are mostly found mint and no matter if there were only 1,000 issued, they go cheap. It does not help the value that they are harder to mount and display. We should not be shocked that they are made to generate revenue and for no other reason. Maybe to appease a specialized group but mostly to make money. Not the greatest evil. You will be hard pressed to ever use one as postage and have it seriously considered as a genuine non-philatelic usage. The pricey Russia SS's from the 1940's can be found on cover but are all to or from dealers of that era. They dress up a collection though kind of like proofs/essays and other ancillary material.

Although I don't collect them, I've seen a good number of souvenir sheets in Scott's in the period from 1920 to earlier 1950's from places like Germany, France, Belgium, Switzerland, and others. Many have quite high catalog value- multi hundreds of dollars. Do these not sell well?

The three pre-WWII French miniature sheets fetch decent prices, as do the individual stamps from them. There are plenty of used copies, but with bespoke exhibition cancels, rather than genuine postal use. But issue was sporadic, whereas now there are frequent French miniature sheet issues with, in turn, a smaller "souvenir"sheet.

The terms souvenir and miniature sheets are used interchangeably. Philatelic bureaus are calling everything a souvenir sheet. They, however, are just a miniature sheet with a mix of stamps. The African sheets OP refers to are mainly miniature sheets.

Many of the valuable early European souvenir sheets were issued as souvenirs from exhibitions and not widely available.

Probably the rarest SS of them all, the Russian souvenir sheet of the 1932 All Soviet Philatelic Exhibition in Moscow with the unique three line personalized overprint "To the best shock worker of the All Russian Philatelic Society - President of the Moscow Philatelic Organization E.M. Nurkas.

From Cherrystone:




Sold in 2008 for $776,250 including tip.