In my personal opinion, neither you nor any other Mustachian should contribute to a 529 plan unless they currently have 100% of all future retirement spending funded. I'm still not sure if they are a good idea even if you do. They can be useful automatic savings plans for spendthrifts, but that is an entirely different topic for some other forum.
1) You don't have any kids yet! Nothing is certain in this world.
2) You have no idea if your kids will need the money. They could get full scholarships, or more likely in my opinion, higher education will have RADICALLY changed by the time they are college age.
There are tectonic shifts happening in education right now and I agree with a lot of brilliant people in the field that there will be ~free education available 20 years from now that is far superior than what is available for ~$70k/yr at MIT, Yale, etc right now.
You should pay yourself first even if I am wrong about future paradigm shifts in education. I'm not a huge Dave Ramsey fan but he does a decent job explaining here: http://www.daveramsey.com/mobile/article-view/category/investing/storyID/retirement-or-college-funding-which-comes-first-/
To back up my education perspective, here are just a few of the organizations that are disrupting eduction right now:
These also happen to be excellent Mustachian sources of education.