>My spouse and I currently have around $550k in retirement savings across all our accounts, plus another $200k in home equity.

You can count house in NW, but don’t count it as part of retirement savings. You can’t buy groceries with a house, well you could but you’d have to sell.

>This year, I'm on track to save roughly $45k using a combination of Roth IRAs, 401k and mega-backdoor Roth.

That’s awesome. Most people can’t get near that level of saving.

>OTOH, the average American only has roughly $100k saved for retirement.

Ignore that nonsense data. You aren’t them. You are ahead some and where they are is irrelevant.

>My spouse and I have estimated our current expenses at about $60k per year, including the mortgage.

To keep that level of spending you take that multiply by 25 and that’s what you need to not work while your money is invested. You’d need $1.5M to meet a $60k goal. (This is based on the “safe withdrawal rate” of 4%)

>My spouse has some relatives who belong to a vacation club and basically live in resorts in the Caribbean for much of the year. My spouse would like us to sign up as well. To do that, I would need to cut our retirement savings rate in half at least.

Ehhh. First off what’s is the relatives financial situation? Have they reached financial independence(“FI”)? Not trying to be a dick, but you guys haven’t reached that. You are behind in reaching a reasonable FI number for yourselves. Once you get to that FI number (the $60k/$1.5M) does it support living in another country part of the year?

>My parents will leave me and my sister $500k each when they pass on in a few years.

Don’t count on inheritances. You never know if parents need long term care which can destroy inheritances