To answer some of the questions for context.
Net worth is approximately $2.1 million. Paid off house worth $750k (Boarder just cried, I know). $1.3 million (rounding) is invested, $900k in retirement accounts and $450k in after-tax account. We will move to a lower cost of living area at some indeterminate point, which will unlock some of the money in the house as well.
My spending figures do not include taxes, but no state income tax, so whether the extra $20k goes in the retirement account really impacts the total tax we'll pay.
Looking back at the figures, spending is likely to drop to around $70k once I stop working. If I take the dividends from the taxable account (rather than reinvest them), my wife's salary plus the dividends will come close to paying our annual expenses. So it's primarily a question of whether it's better to put $20k each year in the retirement account if it means coming up with the $20k from the $450k taxable account. That's the one I'm not sure about.
I'm pretty sure we're set financially. We've already accrued social security a federal pension worth about $50k starting at 67, and I would guess our annual expenses at that point with kids out of the house, lower cost of living, etc. will be close to that. Also, with the money in the market for the next 10 years or so, statistically it's likely to double, although obviously that's not guaranteed. Regardless, we're not tapping the investments so long as my wife works. It's just a question of whether to effectively shift $20k per year from the taxable account to the retirement accounts.
I appreciate the input. My instinct is to continue maxing the retirement withholding just because it's tax advantaged space, but part of me thinks that if we're at the 12% marginal tax rate with only one salary, maybe we should just pay the 12% tax now on the theory that it's unlikely ever to be much lower than that, and also buy ourselves some flexibility with the money (kids college, etc.).