I think that question you should ask yourself is:
Will you use your base code somewhere else except Android?
If you want to share code between desktop/Android/WP/iPhone and want to have same functionality and only change GUI code for each platform then I think you should go for it. Just keep in mind it's proprietary software base on Mono. Mono is kind of unwanted child in Linux sphere but Miguel made good job and discovered good way how to make money on it by doing MonoDroid and MonoTouch.
IMHO if you want to make Android only applications just use Java. You know already C# and .NET. Trust me going C# -> Java is not hard. You'll spend most of the time in Android API anyways and difference in syntax between those too is just so small that you should not be worried about. You'll surely benefit more by learning Android API and framework than thinking if you should use C# and MonoDroid ;-)