I currently have slightly less than you in a Vanguard Target Retirement, and while I could lower my fees slightly by switching to individual index funds, I don't yet have enough in there to qualify for Admiral Funds in anything except the largest chunk (total stock market) of the asset allocation, and in order to meet Vanguard's 3k minimums, I would need to buy more bond fund than I want to have in bonds. Also, I like that my target fund automatically rebalances the asset allocation as the market changes. I may move to individual index funds in a few years when my account is larger and I could qualify for more admiral funds.
The other posters are correct that you could lower you're fees by switching, but 0.18% is not bad, and Target funds do have some advantages. If you do want to switch to individual index funds, make sure meeting the 3k minimum for a certain fund won't mess up your desired asset allocation and tilt your investments more than you want towards that fund. And think about whether you will be diligent about rebalancing yourself.