I agree with the conclusion that Rayvt came up with, but, not necessarily the reasons.

1st off, the bookkeeping is a nightmare, to keep track of the after-tax amount.

As far as I know 401k and IRA administrators will take this into account when you withdraw and it is just a matter of reporting the correct amount on tax return.

And you get screwed by the IRS on the ratios when you take withdrawals.

I don’t think you get screwed by the IRS (any more than usual). If you pay taxes before contributions you will not be taxed upon withdrawals.
Generally, I don't think it is a good idea to put taxed money into a tax deferred account unless you need the space for tax inefficient investments.
In your case I suggest you look forward to your withdrawals in the future. You indicate you plan to retire before age 55. At that age you would pay penalties on withdrawals from tax deferred accounts. It would be better to have a taxable account to take expenses from during this period.

Bob