I think what you ran into is that there aren't that many owners with cars sold without superchargers enabled that also know about the chademo adaptor and want to buy it, so it's not something that comes up often for those guys at the service center. Couple this with the changes they've made to the policy and price for using it with non supercharger enabled cars, and the price changes for the adaptor itself, and you've got a wad of confusion. You'd think they could just look at the current info in their system and that'd be that, but I suspect (without hard proof) that their system has burned them in the past by reflecting not up to date or inconsistent information. So sometimes there is this conflict behind their direct experience and their different documentation sources, and it leads to the unfortunate interaction you saw.
Odd to consider, but we here often see more of tesla than the average guy at a service center does in some ways. I expect far more people have posted here and talked about their chademo experiences and interaction with tesla than the single service center has ever seen.
I'm glad you got an answer, though sorry it wasn't the best one for you. It's funny, but I'm pretty sure I remember at one point before they had lowered the price, they had said they were removing the charge for enabling it (but not Supercharging). Then I guess they lowered the price and no longer wanted to throw it in. Don't know if that was just talk, invented memory, or if anyone ever actually bought one at the higher price but then didn't have to pay to enable it on their non supercharging car.
If you ever decide you might take many trips at all, supercharging is absolutely worth it, and I'd definitely do that before doing the chademo adaptor. Afterwards you could always add the adaptor too for just 450 if you felt the supercharger network wasn't enough, but it's already arguably far better and getting more so.
btw, I had more regarding service center interactions, but it got long and too preachy anyway, and was increasingly off topic for this thread. I split it out to
here