For many many people, getting the CHAdeMO adapter is more about opening up where they can go (in BC) than providing a secondary charge option if Superchargers are full. It was 100% necessary for our tour of Vancouver Island the way we did it (i.e. not constantly looping back to Nanaimo). It was also necessary with our route into the states from the Okanagan valley (the gap between Superchargers is just too much except for the most ideal circumstances... and we went in Winter). Not to mention all the other places we can now go - east, north, to a bunch of smaller towns and less-traveled routes. Supercharger infrastructure is simply bad for all but the most primary routes. Fortis and BC Hydro have really rapidly deployed these stations and it's fantastic.
I'd say free CHAdeMO stations have almost half "paid" for the adapter. This won't be everyone's case. The value to go many more places is what got us to buy it.
I actually don't recommend getting the adapter to avoid Supercharger lines. Most places only have 1x CHAdeMO plug available. First, good luck not waiting for that during peak travel times (when Superchargers are busy, basically), and second, good luck not pissing off other EV owners who think Teslas should just use Superchargers and leave the limited number of plugs per site for the other EVs. You'd probably wait in line longer at a CHAdeMO station if lines existed at the Superchargers.