Putting a value on these is difficult for several reasons. First it's my experience that these are not exactly what I would call collectible, I've never been asked about buying one and I sell a lot of collectible gas pumps.
However that's not to say that someone might find them interesting to set on the shelf.
From a salvage standpoint I don't see many parts that could be used on a clock face pump.
From a actual commercial use of these, I have no idea if there is a market for them.
If your looking to sell and have no idea of value I'd stick them on eBay at a low starting price and see what happens, to me that would indicate if they have value.
Tom.
I agree with all your comments. You don't see much of a market for meters like this.
They are cool hardware, I'll probably clean them up and display them in the garage.
There is a similar meter for sale on Ebay now asking $325 Buy It Now. It looks more like a unit used for water. Here is the search info; 1920's TRIDENT BRASS FLOW METER w/SIMPSON LARGE DIAL GLASS FACE - gas / water
I found the units in rural eastern Colorado at an old closed down Diamond Shamrock.
Thanks for the response Tom!