What is your site for? And what is your main goal for your site?
If you answered those questions, I could better answer your question. I believe that a mailing list is a great idea to let your members know about you and your brand (even though you aren't necessarily selling to them) so you aren't doing anything wrong! It's just a matter of if you are willing to pay to show your members free content or not.
All in all, I do believe it would be worth it. Hope this helps!