Okay, I hunted up some contact information. In the past, I would have said that snail mail is the most effective way to get your voices heard. The theory is that anyone who takes the time to hand write a letter gets more attention than a hundred emails.
But...I found this
message board for Journeyman, where the members are concerned about rumors of the show being canceled, and someone there has posted some extremely helpful advice about TARGETING the right person to contact.
That led me to
THIS listing of who at NBC is involved with Las Vegas.
According to this list, the target person would be one Kellie Kulikowsky.
However, I don't know that in this instance we have any worries about a show being canceled, or any urgency about contacting anyone, but rather we'd like to let someone know how much we loved seeing the MPI gang back together again, and how we wish there was more of that, rather than the meaningless plots involving the relatively bland and faceless regular cast. I tend to think that snail mail would be sufficient for this. I mean, put yourself in the shoes of the NBC or Studio people, and ask yourself if you'd want to get spammed by a bunch of fans with an agenda. Indeed, your email might get caught in some corporate anti-spam filter! Sure, snail mail gets filtered by assistants, but even so, someone does read them, and will at least note the gist of several pieces of mail on a similar topic.
My other advice? Keep your message friendly, polite, and brief. That's BRIEF, as in SHORT!! You get no extra credit for length. This isn't a class where the teacher might be impressed by sheer word count. People have real work to do, and they don't have time for long, impassioned missives. The longer your message is, the likelier your email or snail mail gets dumped into the crank bin.
Personally, I'll be writing a snail mail letter to the first name on the executive producer list (who's probably the show runner), and mailing it to the actual production studio, which in this case is probably NBC Universal Entertainment, rather than Dreamworks Television. (Although that's just a total guess on my part. I'm betting that the filming takes place on a Universal lot, and that's where the executive producers have a mailbox.)
The idea is to make the letter EASY and QUICK TO READ. To that end, I'll be using a word processor and sending a printed letter, rather than a hand-written one. Er...that's The Plan, anyway. Real Life might intervene and keep me from carrying through!!