Had a friend who collected slot cars. I think Aurora are the most popular and draw the biggest buck.
There are people who collect Lionel slot cars too. Typically they are Lionel train collectors who have branched out. With a few exceptions, most of the value is in the cars. Lionel did made a few specialty tracks that draw some extra bucks. And the 5160 viewing stand was worth some money at one time. Not certain in today's market.
Here is a link to a page on the viewing stand. Note that the write-up is in error. It claims that the Lionel slot car line was finished by 1963. Slotcars were still in the 64, 65, and 66 catalogs. And Lionel was still offering slot cars to it's dealers in 1968. I have some factory paper to that effect around somewhere.