OP, also look at the effect of the Retirement Saver's credit. You are in the income range to be eligible. If only one of you has retirement contributions, your credit will be less. The first $2k retirement contributions for each of you are entered in the calculation. At your current AGI, you seem eligible for 10% of the first $2k, so up to $200 credit for one of you, or $400 if both have retirement contributions of at least $2k. If you can get your AGI below the next threshold (IIRC, $40k for 2016, may be different for 2017), the rate increases to 20%, so doubles your credit. If you can reach the lowest threshold ($37k for 2016?), it increases to 50%.
The Retirement Saver's credit is nonrefundable, so you can't get back anything over your tax liability, but it can free up the other refundable credits like EITC and CTC.
I look at this process as iterative - how much can I afford to defer to traditional retirement accounts? How much in refunds does that net me? Can I put that additional $ to retirement accounts too? How much larger is my refund now? Rinse and repeat until you run out of retirement account space, or zero actual tax, or chart limitations, or ??
Make sure to put some $ in retirement accounts in your spouse's name. Partially to make best use of the Retirement Saver's credit, partially to spread the balances between you. As a longtime SAHM (now working part-time, still no 401k) I now regret not funding IRAs for me earlier. We view DH's 401k balance as "ours", but I recently learned of a state tax rule that will affect us in retirement: the first $20k of income from retirement accounts PER PERSON is tax free annually. However, it cannot be lumped together in a couple - if I have no taxable retirement income, we only have $20k tax free space for DH's retirement income, instead of the possible $40k. The more you know, the better you can plan.