Thanks to all that responded. Here is some further info about my situation.
I am currently 40, a hands-off investor, comfortable with moderate risk as I'm looking to grow the fund but not overly risk the principal. With that info, any other advice?
Be careful about target date funds. I've done a lot of post graduate work on asset allocation and a lot these funds have too much equity risk. Assuming you are going to retire at 65, then you would probably choose a ~2040 fund. This fund has ~90% equity. That's insane. The 10% bond allocation offers very little in terms of diversification. Keep this in mind. With a 60/40 portfolio, 80% of the volatility comes from the equity side. Imagine what characteristics a 90/10 portfolio will have. Don't be TOO hands off when it comes to your retirement. Do your homework and choose your money manager wisely. It's your financial future at stake.
You have received lots of good answers but I'll add my two cents. A lot depends on your personality. If you are the kind of person who wants the maximum amount of freedom of choice, you will roll the 401k over into an IRA with an investment firm like Schwab who is not part of a mutual fund organization. If you are hands-off you will have to rely on (1) your own judgement (2) someone at the other end of an 800 number or (3) a personal financial advisor who is a fiduciary. If you can find #3 I believe you will have a less stressful life since your portfolio will be custom-built for you, adjusted regularly, and you'll get lots of landholding on the way.
The best option for you would be a "Target Date Fund" Should be available within your plan. You'd select a 2040 fund. This would provide growth now and a protection of principal later as you get slower to retirement. You goal needs to be to 4x your existing account over the next 20 years plus maximize on going contributions.
It sounds to me that the best thing to do is to roll it into the Vanguard 401(k) Plan and talk with them about your risk appetite. They will help you walk through picking the correct allocation for you and at no extra expense if they are administering your Plan. You are correct you should be willing to take more risk right now to help that money grow the most over a long period of time 20+ years.