We have plenty of friends who are the opposite of MMMers, in fact I don't think DW and I have any friends who don't spend like it's going out of style. We have 3 boys, I drive my 2003 Corolla and she drives the 2013 Nissan Quest mini-van. I have received the comment many times about my old crappy car, but I fully embrace it and own it and love that I'm still driving the Manual Corolla w/roll down windows that I bought after College and still gets 40 MPG on the highway, who wouldn't love that! I think most of the time our 3 boys can mask any financial "opt out" scenario, so they are our cover, but nobody will question why you aren't spendthrift if you have 3 young boys, but "spending activities" really don't interest us that much. Our friends drive nice cars, vacation a lot, eat out a lot, pay money for babysitters, buy boats, have pools, etc. I don't want to sound like a mooch, but I love friends who have pools and boats, b/c they WANT to show off and entertain, so we let them! We'll bring beer and chips and salsa, but I don't want to buy a pool or a boat and have to maintain something that's going to give me a headache. I don't want to travel far away w/3 boys and spend a week packing the car for 3 needy kids to spend a weekend somewhere else. That's not fun to me. So the "polite pass" (and I'll literally say those exact words) is fine by me, and between me coaching soccer on the side and our 3 boys, we really always have an excuse b/c we keep busy.
What I find is that when I'm honest and genuine and happy, that people want to spend time w/us, so we're not short on hanging out w/people who want to spend time w/us. None of our friends are mustachian, just b/c it's a small crowd. I can bust their chops about spending sometimes, but I'm also not trying to change people. If people ask (which they don't very often) I'm happy to spread guidance and help answer questions, but typically people don't ask b/c they don't want to change. If conversations about money come up, they can see I know what I'm talking about, but often they don't follow up just b/c they don't want to, b/c they don't want to change. That's not my job though, to each their own.
So I would try to figure out why you want to hang out w/them, if you really enjoy their company. If you do, then suggest hangouts like a hike, having them over to your place for a fire and outdoor beers, take a bike ride, etc. All the hanging out we've done w/our friends over the last 5 years is really minimal spending. We did do a weekend trip to a mountain which was a reasonable price, but other than going to the brewery and having a few drinks while everyone is playing outside, there isn't a ton of money involved. We don't enjoy going out to dinner when we have to get a babysitter or over-spending, as it just doesn't make us feel good. There is plenty to do w/friends that doesn't cost much, regardless of their spending/savings level. I try not to judge, we do what's best for our future and let them do what's best for theirs. Some people want to work until they drop dead, that's fine w/me if that's what they want, that's just not what we want. Friends come in all shapes and sizes, and spend money at different rates, who cares. If they are friends then they are friends, just don't be afraid to have a "polite pass" if they ask you to do something you aren't comfortable with. I polite pass all the time and it makes things so much easier as I've very direct w/my communication (which most people are not), but that just helps strengthen friendships.