It sounds like in the OP's situation the two asset pools are very different, which will probably matter for planning for FIRE.
I treat our pools together, but b/c most everything is in separate 401k's, IRA's, etc, it's easy to separate by individual. Over the last few years i've always calculated our combined FIRE number. But she is not as excited about FIRE as I am, and I don't know if i can wait long enough to hit the combined number. She isn't spendypants, and saves more than the average American, but she isn't really mustachian either. This has raised the possibility that I may FIRE earlier than her, which isn't really an option i had considered before, and am currently thinking about. (i still have years to think about it anyway).
Perhaps the answer to the OP's question comes down to, do you plan to FIRE simultaneously with your spouse or not? If yes, then net worth by couple is probably all that matters, but if no, then net worth by individual is more likely to matter.
This is a reasonable question at least in my case because we have similar incomes and childcare responsibilities, share expenses, etc. A situation where one spouse made a lot more than the other would probably skew this decision.