Be polite and use the contact form on the "contact us" link on the main website. Don't go around emailing directly, I'd actually consider that a breach of privacy. It also depends on how you ask them, and what exactly you ask them. I know though if someone just emailed me and I never gave them my contact info, I'd be taken aback a bit and be way cautious. I just used the method they have provided for communicating with them, and I got a reply.
I'm sure if people start asking "Where's the next Freespace game?" that they'd either trash it or politely reply exactly how other people on these boards have replied. Plain and simple, asking about what coulda been has been awnsered already, rights to such game are held by a company in financial limbo, and probably will never be released.
For my project, all I did was use that box, and when I got a reply from Dan Wentz, I started emailing him directly. I asked a polite question, explained what the project was for, and hoped for the best. I got pretty much everything I needed to make my project a reality. Believe me, Volition knows that we exist, and they are proud of our work. Everyone who has worked on FS1/2 held the game close to thier hearts, and they think highly of it. We, the community have awnsered everything though about a future installment, and honestly, it'd be a waste of time to bombard V with these questions.