I struggle with this kind of stuff too, I'll have drafts sitting around forever while I ruminate on my writing. Asynchronous communication provides the opportunity for perfectionism, and I have trouble resisting the urge to over-edit.

The best trick is to parlay it into another medium, or at least send a brief acknowledgement of receipt. Taking a complimentary tack works well: "Your question was so insightful I will have trouble conveying a satisfactory answer unless we chat"