It's actually not about living at a certain frugal-ness. It's about figuring out what you spend, and then on top of that deciding what things actually add value to your life. Like Cad said, if you need $100k in post tax income to be happy, that just means you need a larger portfolio to support that (and potentially working a lot longer).
My wife and I feel like we live incredibly spendy lives, but that still ends up being under $50k a year. We built a home gym last year and went to Disneyland 4 times (we don't live close enough to stay there, so hotels are included), we spent 2 weeks at the Gulf Coast beaches visiting my in-laws, we go hiking regularly, and we spend something like $450 a month on groceries. But we also rarely eat out and keep our thermostat at 63 in the winter, because those things aren't as important to us (I'd rather wear a hoodie around the house than blast the heat all day). We drive older cars and I do most of our home repairs myself (patching the roof, re-doing electrical, plumbing).
We have a $140k income, but live like we're on a $50k one. That means we max out IRA's and 401k's, and we're also starting a taxable account this year. I'd definitely say MMM's principals are easier with a higher income. It's kind of the core of what this discussion is, though. Most people can probably live on under $60k a year without sacrificing much, if anything. That means any additional income can be saved, and even better, means you need less to retire on (since you have a upper threshold on what you require for a comfortable life).
