How do you price based on value without a corollary to tokens? If you charged $40 for this service then maybe you don’t provide enough value for the casual user who does the occasional school report. On the other hand you may be unprofitable for the doctor that decides to dictate all of her interactions every day or the author who dictates an entire book.
A customer sees "word count", they understand what's going on perfectly, right away. Tokens? More than half of them will think "what, like, game tokens? do I have to buy them in advance?"
Generously, 10% of potential customers are going to have even an approximate idea of what a token means in this context, maybe 1% could tell you that words and tokens aren't quite the same thing.