The original owner opted not to help support the build out of super chargers, A choice he could make. Tesla has no obligation to suddenly start giving it to people. And, I am certain that you're charging would be free unlimited for life, as that's what the car was sold as, should a person upgrade to the option to supercharge.
I get where you're coming from, I've been frustrated with Tesla more than a few times, but this is the position from long ago. They don't change easily! They are a very top heavy organization, with Elon Musk deciding pretty much everything. It's just what is.
As to whether the 2500 is worth it to you, you'd have to decide how many trips you might take where you would supercharge. A 60 isn't really a great road car anyway, with the range being somewhat limited. However, it would make a nice City car. I think you are correct in just not paying for supercharging and using it around town.
Alternatively you could pay somebody like 057 tech to put a 100 KWh battery in it. That would make it exceptionally useful, but you'd be out a whole bunch more money again. With the used prices of Tesla's coming down, it's probably wiser just to buy one that has all the options you want.
One other thing, 057 tech and recell both have warranties for the Tesla batteries. Might be worth it to you. Especially if you do go for the supercharging option.