Yes. But...
What is really beneficial for you as high-income earners is putting money in traditional 401k or traditional IRA accounts. Every dollar you invest in a traditional IRA / 401k has an immediate 25% gain due to not having to pay taxes on it. However, because you earn so much you are not actually eligible to deduct you traditional IRA contributions from your taxes, so that benefit goes away.
http://www.irs.gov/Retirement-Plans/Plan-Participant,-Employee/2014--IRA-Contribution-and-Deduction-Limits---Effect-of-Modified-AGI-on-Deductible-Contributions-If-You-ARE-Covered-by-a-Retirement-Plan-at-WorkWhat would be best for you then is for you both to contribute the maximum you can to your 401ks, currently $17,500 / year each. Then, after that's done, if you still have extra money to invest then yes, contributing to a Roth IRA is stlil better than just putting things in a regular taxable account (but not quite as good as a traditional IRA unless you're planning on spending *a lot* of money per year in retirement).
At a max total contribution of 11k per year, it is a significant percentage of our investment money that we won't be able to have any access to until we are much older,
This is not really entirely true. There are several ways to get your money out early from your IRAs / 401ks without paying the penalty. One is to take Substantially Equal Periodic Payments from it until you reach retirement age. The other is to enact what is known as a "Roth pipeline", see here for an explanation:
https://forum.mrmoneymustache.com/ask-a-mustachian/help-me-understand-the-roth-conversion-pipeline-idea-and-its-benefits/Even if that's not true and you do have to pay the 10% penalty, if you're withdrawing money because you retired early then it's still probable that your average-income-tax-rate + 10% penalty will be less than your current tax bracket of 25%, therefore making it still profitable to use tax-advantaged accounts.
and is thus unable to help with any fluctuations in the market.
Well I'm not really sure what you meant by that, but I think you're wrong. If you mean that you want to withdraw money from the stock market when it's high and add money to it when it's low, then there are two problems with that:
1) it's virtually impossible to tell when the stock market is high or low. If you could do that you could be a billionaire investor. "The market can remain irrational longer than you can remain solvent."
2) you can do that even if your money is in a 401k / IRA. Simply transfer money out of your stock mutual fund and into a bond mutual fund, or REIT, or gold fund, or whatever (in the 401k's case: assuming that your company has provided those options). The only thing that having money in a 401k / IRA prevents you from doing willy-nilly is taking money out and putting it into your checking account.
But regardless, by leaving your money in "for the long haul" you *would* be riding out the fluctuations of the stock market, and therefore getting the average annual return from the stock market. The problem people have with fluctuations is that they sell all their stock right after a crash, which is the absolute worst thing you can do. To many people, the more inaccessible their money is the better. You may want to read up on "dollar-cost averaging" for a more full discussion on the topic.