Being close to replacing the rear tires is true even if you have brand new rear tires.
Without a doubt, I spend more on tires than on electricity.
The main thing to check in a used Roadster is the condition of the battery. How many miles does it show at full range charge? Other than that, there's not all that much that wears out.
You also have to be prepared to talk with strangers in parking lots all the time. My experience is that it's usually neither babes nor lunch ladies so much as guys who are into cars. I'm pretty much always happy to talk about my car, so it's not a problem for me, it's just part of the Roadster experience.
And yes, getting in and out can be a challenge. On the other hand, I managed with a pretty bad knee injury last year that meant that I couldn't bend my left knee for a few weeks. The opening in the door is smaller than the distance from my hip to my foot with my knee straight, so I had to get in by sitting down with my legs sticking out the door, hoisting myself over into the passenger's seat (while not destroying the parking brake), rotating my legs in, then hoisting myself back into the driver's seat. Then reversing the procedure to get out. I really happy when my leg started working again.
And I also have to agree with everyone else: don't buy a Roadster without driving one. It's a very different experience from pretty much every other car, and it's not for everyone. (OTOH, I guess I paid for mine before I'd driven or even sat in one, but that was the early days when they just weren't around. And I was pretty sure I'd like it, which I did.)