Is there a way I can import ReadItLater's exported html file into my Instapaper?
Though I don't have a tool now, I guess it can be done in couple of ways. Yes, no one click solution.


Email each url to your personal instapaper id (Refer this Lifehacker article)
Can parse your export list and use simple API from Instapaper to add the links to your account. Refer API docs




Update:

As I said earlier, it is not a one click solution but doable. As a matter of fact, I did create an extension for chrome to do this. Here is the link http://minus.com/mc3va2C

Update 2:

The source of the extension is available @ https://github.com/palaniraja/RIL2Insta