The 1930 edition of the Scott catalog listed all the stamps of the world in one 1,700 page, 4x6, two column volume (today is six large volumes). Prices were interesting. The mint ten cent type IV of the 1857 US issue (Scott #34 mint) cataloged just $300. Today we know that there are fewer than ten of this stamp with original gum, and a decent copy would sell for $30,000. But just five Scott numbers later is the #39 which at $1,000 in 1930 is nearly the same as it catalogs mint no gum today (2015 cv $1,100).
I’ve never seen the story written up on why the high values (24¢, 
30¢, & 90¢) of the 1857-61 issue mint have performed so poorlyin the last 85 years, but I can hazard a guess why. These stamps were demonized in 1861 at the beginning of the Civil War to prevent stocks that were held in rebel post offices finding their way North to be sold for hard currency that the South needed. There were always largish stocks of these in dealer hands for the 1870s onwards as demonetized stamps found their way out the back door of the Post Office, after they were returned by post offices after demonetization. Governments tend to do very well preventing counterfeiting and theft of stamps and currency that have negotiable value. And governments tend not to care too much when these stamps are demonetized.
The best investment of all in 1930, if you could have made it, would have been printing futures for the Scott catalog. The 1930 edition had a retail price of $2-that’s two dollars for a Scott catalog that listed every collectible value at the time. Today’s six volumes of Scotts list for $820.