Just to clarify, you mean that the amount an individual can put in a 401K doesn't change with marital status. I read it as a married couple (two people) can add the same amount as a single person, which I belive, is not what you were trying to say.

By it'd nature, a 401K is an individual account. Contributions come from a single employee's pay check. This means that you can put up to $12k in your account, and your wife $12k in hers, providing your AGIs does not limit your contribition amounts.

While you both have 401Ks, you can not also deduct contributions to a traditional IRA (which again is individual, not combined). Since your wife would be taxed if rolling her Trad IRA into a Roth IRA, I recommend leaving the IRA as is unless there are costs or poor investment options that might drive you to change.

If you have maxed contributions to your respective 401Ks (or at least the minimum to earn any matching contributions), then consider a Roth IRA. Just remember that Roths are after-tax contributions. All your tax-free contributions will come from your 401Ks.