I can't ever remember regretting buying dinner for a lady. I enjoy the company of women immensely, and if my punting circumstances were different, I think I would always try to include dinner in a punt.
On that subject, increasingly I notice punters focusing on at least trying to make punts mutually enjoyable, so towards that end, why not give a lady the option of dinner first? Surely a punt is better for both parties if there is some familiarity first? Why not make it an experience, rather than just a shag?