First: Stop nagging her. (And if you aren't, kudos to you. I started this by nagging and it got me nowhere.)
Second: Do a budget. Start tracking spending using the website for whatever bank you have. Spend time getting to know what your monthly expenses truly are. If your situation is like mine, you'll see your wife spending you down to $0 every month. Don't get mad, just get familiar with what's happening.
Third: Rank your expenses by size. Biggest to the smallest. Starting with the biggest, ask yourself "what must I do to reduce that expense?" If it's mortgage and you can lower the payments by refi, then refi. If it's cellphones, then when the contract is up, swap out the cellphones for very inexpensive month-to-month plans (I went with Republic.)
Guess What: If you are like most households, your wife's spending won't be the most expensive thing. It might not be in the top 5 items at all.
Repeat Third step above indefinitely, BTW.
Fourth: Open a new account at the bank you use. (with or not with your wife. I don't care) Start electronically routing your newfound savings into that account and start amassing money. Don't hide it from your wife (tell her if she wants to know) but don't volunteer it either.
Now, here's where it gets crazy:
Fifth: Ask your wife what experience she most desires, that costs money but is reasonable and affordable. Is it a beach trip you've never been able to take? Is it the honeymoon she wishes she'd had? Is it a visit to go see family she's not seen in awhile? Is it an upgraded, used minivan to replace the beater one she's driving the kids around in?
Sixth: Team with your wife to achieve that thing. Set a date to achieve "the thing" by an agreement with your wife, and have the both of you strive to make that accomplishment. Work with her to achieve something SHE WANTS.
Now watch her take off like a lean, strong MMM racehorse. Once you team with her and give her your strength, she will surprise you at how she finds savings, moves money around and generally does whatever is possible to make the goal.
Then, when you have enough money saved, you execute on the goal.
Now, here's the magic part:
a) You oversave a little bit for the object/objective, with the intention of leaving yourself about $1k "seed money". That will begin the savings for the next "thing".
b) That next "thing" can be whatever it needs to be, but it should be something like eliminating a debt or wiping out an expense in order to generate more cash flow. Set the objective like you did before.
c) At some point, move the money from the account and invest it.
Notice that nowhere in this process do you "nag the wife about money". What you do, instead, is focus on wants that make sense and work together to become a team to achieve that goal. Then, since she DOES love you, she'll want to reciprocate and help you achieve a goal that's important to YOU. And of course, YOUR goal will be some mustachian "thing": increasing your 401k contribution, opening a Roth IRA, etc.
This is how I was advised to do this by a co-worker who originated the process with his own spouse. I used it in my situation and it changed things forever.
Now: My DW is not mustachian and never will be. But she understands the power of these principles and no longer fights me on them. In the meantime, my 401k savings rate went from 3% to 21%, I have Roth IRAs for both of us, a post-tax investment account, emergency savings, and I manage to make a big payment against the mortgage principal twice a year.
Most importantly, she knows I'm doing this financial work for the both of us. Not to amass money then drain the accounts and leave her. Because that first project we teamed together on strengthened both our financial picture AND our relationship. I PROVED to her that "I'm in it for you" and demonstrated it clearly.
Now: your process might vary from what I've written above. But the point is the same. Find out what she most wants, use the MMM principles to save money and pull cash from your income stream to an account you designate specifically FOR that want. Then when you are done, go out and get that want and give it to her.
In the meantime, you streamline home finances while this is going on and when "the project" is done, you've got more headroom for approaching the MMM lifestyle.