Nice!

However, this style of go-faster "Streamline" type wasn't just for cars, it was also used on other slick products, eg refrigerators:

Does anyone know who originated it?

Nick,
I don't know who invented it but my guess would be that it came out of a need due to the cutting and casting of metal and the ease of mounting it on products. If you think about trying to speed up production of products such as the icebox and wringer-washer as well as bicycle and later automobile, it makes sense for this to come about. If I want to mount product lettering, I need someone with spacing skills if I use individual letters. If the entire brand name is one piece, the skill and time needed is much less. These things were then cast in pot metal and mounted as a unit. The casting and removal from moulds requires some adjustment to the design so that metal flows into all the areas and can also be removed from the mould without damage. This brings about the tapered edge and rounded corners we see in these brand markings. Also, stroke contrast was limited by limitations in casting. The typical script written hand joins and tighter spacing were ignored in favor of a strong, flatter baseline join and wider spacing required to make a workable mould. ( With todays materials and injection moulding techniques, we no-longer need to be so limited by early 20th Century casting issues.) The straight line baseline also made mounting easier since all mounting holes and guides could follow a straight line.
For a timeline, I would guess this kind of lettering came about in response to factory production assembly-line techniques. This is more in the 1920s and 30s than 50s although assembly line techniques really blossomed in the 1950s.
To me, that makes the designer of this style to be some cooperative work between the metal smiths and early "efficiency experts" who just did what they had to with the materials of the day.

I like them, but find confusing that two styles so different are presented under a single typeface name.

http://www.theonion.com/articles/artists-announce-theyve-found-all-the-b...

Advantages of streamlining vary with the speed desired. Unless the car is to operate at more than 45 to 50 miles per hour the advantage is slight. If the car is operated continuously at high speeds the fuel saving is worth while and is all in favor of the streamlined car. automotive diagnostic tools