I agreed with hiding people’s email address. But how about a question on the sign-up sheet asking if they would like to be e-mailed with a reminder for next year. Then we could save the addresses, and two weeks before sign-ups open drop a note to everyone reminding them of signups. Not everyone goes to the site and takes part and this would help us with reaching those hikers.
Other than that, I can’t think of anything else that we have not done before.
Given that… I think it will be ok to e-mail last year’s participants, but with a “leave me alone” option in the e-mail.