Just the other day I wrote an article about LEGO HO Scale 1:87 Cars/Trucks of 1955-70 for the Brickset main page.http://brickset.com/article/14184/lego-ho-scale-cars#comments
(Warning: if you don't check out the above link... the rest of this thread may be a bit confusing... ;-) )
Because LEGO made such high quality plastic cars, Train collectors would often collect them as well as LEGO collectors. However, because of LEGO being extremely popular... the value of 1:87 scale LEGO cars and trucks is often higher than that of other old scale cars/trucks.
Here's an example of a (non-LEGO) train auto hauler hauling several hundred Euros worth of LEGO Beetles...
From 1955, when the first LEGO Bedford Trucks came out, until about 1960, TLG promoted the use of their Town Plan System with Märklin and other HO train sets. This was often displayed in later 1950s LEGO catalogs.
Here is a 1958 Retailer display window "slide" (lit from behind by a light bulb) image showing the combination of LEGO 1950s Town Plan boards, LEGO 1:87 trucks and HO trains.
Many of the building models shown here were actually glued display models that were sold to LEGO retailers. Several of these retailer model catalogs in my collectors guide, show these glued models. And often they find their way into LEGO Idea books as well.
The 0753 model shown in this Blue Retailer Glued Display Model catalog page, was used in 1961 as the main model for the 810 Town Plan Set of continental Europe, Britain, Australia and Japan.