I'm in a similar spot of wondering if I should put more into my 401k but mainly because I still want to maximize the Saver's tax credit.
With the new standard deduction being 12k for married filing jointly and only making 50k, I'm @ around 38k, which seems to be the magic number for getting 50% back on up to $2000. In practice, it's hard to get the full amount but for 2017 i got about $1600 by contributing to a spousal IRA.
So, I've started making ROTH contributions to my 401k instead of the Traditional 401k deferred contributions. As far as I can tell, I want to have a tax bill near $1600(saver's credit is not refundable; can only reduce taxes to $0) while having an AGI that does not exceed 38k...not even by $1. To do this I contribute to an IRA for the previous tax year to get it right, if needed.
So, if your AGI is near 38k(and you're married), I'd factor in how contributing to a Traditional 401k/IRA would impact the Saver's credit. It might make more sense to switch to ROTH contributions.
This is what I do, if I'm missing something please let me know.
Also, there's the EITC(earned income tax credit)...but I don't have any kids. This would probably change or even nullify my advice but I don't have kids to really utilize the EITC since the Saver's credit is higher than the EITC Married without children.
Bottom line, still max out your 401k if you can, but consider ROTH contributions for tax purposes when you factor in the credits.
links
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-savings-contributions-savers-credithttps://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit