Are you a millionaire when you and your spouse hit $1M net worth, or when you've got $1M each? It's really kind of a silly little semantic nitpick, but I was just curious.
I'll kind of "silly little semantic nitpick" right back, you mention the options of a combined net worth of both spouses of $1 million (implying combined finances) or $1 million each (implying separate finances), but no mention of a net worth of $2 million for a couple; under the second scenario could you consider someone a millionaire if they had $1m+ alone, but their spouse did not have an additional $1m?
Interesting question. Since many things are shared (house, utilities, etc.) but other costs are higher (health insurance, food, etc.) when married, can we compromise on $1.5M?
For us, as you say, there are many things shared (housing, utilities and the like), but we do not see higher costs in the areas you mention; in our current arrangement it is cheaper to both be on one's insurance plan (and in my last job it was even cheaper if both spouses worked for the same employer) and I not sure how getting married increases food costs, our food and preparation costs have either remained constant or gone down (same food, maybe a discount for lager packages . . . and cooking more food at once).
In the end it depends on what our goal is for defining a millionaire . . . if purpose is to identify someone who has done an impressive task, and it is easier to save when combining expenses, then the number should be higher (2.5m+), but if it being used as a substitute for a big ball of money one can live off, then the shared expenses would argue for a lower point (like your 1.5m).
My thought is 1 million household networth excluding primary residence cars and anything with depreciating value (do not count that Timex watch but should include Patek Philippe at fair market value).
This comes back to my point above, what are we trying to get at when we define a millionaire? All of the items you call out by name are relatively easy to tell and relatively easy to determine the value of; so if we are aiming to define an impressive feat of accumulation why would we not include them, but if we were aiming to define a millionaire as someone with a pile of assets they can live off of without any major lie changes . . . then maybe those things should be excluded.
If you don't exclude those items where do you draw the line; is grandma's table that you could get $5-25 for in your net worth?