Thanks to each of you for responding and for being so thoughtful.
In response to your questions and comments:
sometimesinvestor: I do not have a Roth 457(b) available. But I'm thinking that I should lobby to have one made available.
letsgobobby: Yes. I work for a government agency.
bobcat2: I should clarify my pension expectation - the amount is based on my highest five years of earnings and the number of years of service, and includes an annual COLA. If I remain a member of this pension plan until I am 67, I will receive about 65% of my top salary. I am a professional and a manager and have been subject to a salary freeze for several years (which appears ready to lift). Given this, I believe there is significant potential for my earnings to be significantly higher in the future.
BL: I am in complete agreement that I should maximize my HSA contributions - especially since covered expenses from the HSA will never be taxed.
Garco and Ged [earthsea?]: I appreciate your reminder that I am not likely to successfully predict our future tax bracket in 25, 35, or even 45 years (assuming we survive that long). As I pondered your comment and challenged my underlying assumptions, I found myself considering an infinite branching of future possibilities. This led me to conclude that I should probably just accept the simple answer, fund the 457(b), and be done with it. If it's the "wrong" choice, no big deal - at least we've saved money for the future.
In terms of Ged's comment about the potential for delaying SS, I will have to think about this. My initial thought is that we are likely to have significant taxable assets at retirement even if I maximize my 457(b) contributions (due to increase earnings and inheritance). Plus we will have my pension, which should be more than enough to live off of (especially once the mortgage is payed off). We live pretty simply, and I don't see that changing too much as we get (even) older. I recognize that things like unforeseen medical issues among other things might complicate that picture, however.
Also, I don't think a contribution this year and/or next year will have a tremendous impact on our taxable assets. Once both kids are in school full time (public school), our day-care costs will decrease significantly and my wife will be able to significantly increase her work hours (and income). Plus I am likely to be earning more as well. If this is correct, our increased earnings will go to the 457(b) and we'll leave the taxable accounts alone (more or less).
ruralavalon: I fully agree that fully funding our Roth IRAs is our first priority. And I intend to maximize my 457(b) contributions with future earnings increases. And I now think I'm agreeing that I should draw down our taxable to fully fund my 457(b).