I have a DH that is ok with being somewhat frugal, thinks it is awesome that I am very frugal. He loves our savings rate, financial stability, and that I have run all our finances to get where we are.
However, there is a unconscious negative reaction to the "R" word - retirement. I can actually see the look in his eyes change to hear that word. His parents were self employed and started down a path that led to complete financial ruin when they took too many big risks to chase a big reward so they could live a lavish lifestyle in retirement (lost more than $1M). That led to many situations that have left him with permanent scars.
This is the strategy I use that has worked well. YMMV. I think some of it is in the 50 steps post.
First, talk about it a) rarely and b) in small chunks.
2) Paint a picture. On a beautiful day say something like "won't it be nice when we aren't working full time and can just hang out and go biking on days like these?" (notice that sentence does not say retirement, finances, or related words)
3) Baby steps. Don't suggest 45 things at once. Example: After sharing great news of our financial check-up/meeting a few months back (he is having positive feelings at this point). I said " I'd feel a little better if we increased you 401k contribution by 2% more. Can you do that and we can revisit how it is working in a few months?" He did. I never mentioned it again (although I will say the number at next check up). A month later I discuss getting a new cc with better reward - but only after I share the good news about one of our account balances.
4) Have a deep acceptance that he will never be as frugal as me. He values some "things" like guitars, bikes, going to concerts. We will never reach a very high savings rate b/c of that (we are at about 36% right now). However he earns 90% of the income in our house, has stuck through crappy work situations to get us where we are $$ wise, and has lived through some very difficult circumstances I can only imagine. I am ok if that means he spends on some of his true passions and retirement is delayed.
5) I never expect DH to do something I wouldn't - ride bike for transportation, eat leftovers, wear used clothes, etc. Then when I do it - talk it up. Like the really nice bike ride I had going to store. (which is usually totally the truth).
6) After announcing all the great news at a $$ meeting/check up (and him still overwhelmed by the awesome numbers). I said, "yea, I looked at a calculator and we could stop working or just work part time in about x years. We'll be making enough from our wad (not retirement accounts, not investments - those are loaded words) to cover our expenses." (notice these sentences avoid the R word, financial independence, etc.)
Then the doubts, change in the look in the eye comes out. I reply - "don't worry, we can just keep saving and don't have to quit (not r word) until you feel like you want to. Worst comes to worst, you keep working and are millionaire (loaded word with positive values that helps the cause). Don't worry - no firm decisions need to be made now." You could really put a cherry on top of it by saying something like "can you imagine how those a*holes at work (or insert appropriate person spouse can't stand) hears you are a millionaire!!"
Then change subject to something positive they like.
*If this sounds too manipulative, my DH has always thanked me for the job I do with stuff and fully recognizes some of his psychological scars hold him back*
You said you have a 50% savings rate and your wife is fairly frugal. That is awesome in itself and expecting more may be too much.
Also, I agree with PP - don't say anything about her parents' spending habits. You are then intertwining 2 issues - FIRE and in-law issues. That leads to a desire to stick up for her parents, which then comes back with her rejecting both points. If you have had a lot of conflict about this issue recently, you may want to wait a few weeks before starting the plan. Good Luck!
