There are four LUGs in my current area (looking to relocate to Phoenix, anyone in need of a senior sysadmin let me know off-list). There's the U(nix)UG with a college, the U(tah)V(alley)LUG, the P(rovo)LUG (the first to take upon themselves the name of PLUG, which is why they own the domain), and the S(alt)L(ake)LUG. SLLUG is exactly what you seem to envision MPGLUG being, the same thing as PhLUG, but for people who don't want to drive 40 minutes to attend a meeting.
Here's how things played out with 4 different groups--it's all the same people and they just go to the meetings they want regardless of who is hosting or where it's at. SLLUG, and UVLUG don't do much because they just don't have many active members. PLUG holds monthly meetings, typical attendance is in the single-digits and the Salt Lake guys won't drive down unless it's of particular interest to them. As it turns out, meeting attendance is always the same faces regardless of the UG, it's all dependent on the quality of the meeting and whether or not it's interesting.
As for the mailing lists, people gravitate towards the most helpful list that contains the most interesting topics and pertinent conversation. So, people on this list are perfectly within their rights to ask you to stop your emails because it's making the conversation on this list worse and detracting from the technical discussion that should completely dominate a LUG mailing list.
You want to announce an event on another LUG list, that's friendly because it's relevant to people's interests. You want to tell people about your mailing list once, and then bring up the same topic of conversation on the PhLUG list for discussion, that's fine too. You want to troll for sponsors and members, that's rude as it detracts from the quality of the discussion on the PhLUG mailing list. At the very least, you should start including a tag in your email like [OT] so people can automatically filter it into their spam folder.