The more you use something the more it makes sense to spend on it, assuming your extra spending is getting you something. If you used them significantly for two years, it sounds like you got a lot of value out of them.
To be clear, I would pay even $350 for them, if only I could remove the $5 battery and replace it cleanly. Or even bring it to an Apple Store and get a new battery for $30, in a similar iPhone workflow. It just feels such a robbery otherwise.