Of course we all know why TfL cash fares are deliberately set high. But I think that's a very good idea you have about handing out a leaflet.
It would also be nice if when it wasn't too busy, that ticket office staff could offer tourists an Oyster card instead.
The prices are high to discourage people buying paper tickets I presume, which is fine, but for someone visiting (whether from abroad or another part of the UK), they may not even know about Oyster and the fact they're paying a premium for buying from a machine or ticket window.
If they knew it was half the price (well, more than half price) for getting an Oyster, which they can keep and use again and again, then it would be worth it.
I'd personally rather pay £10 for a prepay card, and leave money on it - even if I wasn't sure I'd ever use it again (or even come back to that town/city) out of principle than pay over the odds. For one, if the visitor Oyster has any special designs on it, I'd have one as a souvenir anyway.
There's no point charging more to discourage people buying paper tickets if the people aren't being discouraged simply as they don't know there is an alternative and just think our transport system is
grossly overpriced.