In that light, I have signed up for Authorgraph that will allow me to send signatures that can be kept with electronic copies of my book. I doubt it will ever increase the value of an e-book like it can a real book, but for some people, it is still awesome to know that the author took the time and they have something from them.
That being said, if you give me a little information in your Authorgraph request, will personalize my response. If you are going to take the time to ask me to write you something and sign it, I will take the time to answer something real back.
You can start your author collection for free. It currently costs nothing for authors and enthusiastic readers to sign up. Get your author collection at https://www.authorgraph.com/
I hope to see you there!