Yes, it would be more awesome for at least a few people, as would almost any of the multiple feature requests posted here or emailed to me privately.
It’s not as simple as just making the select box a multi-select, as there would need to be some major code changes to the way the contact form is processed.
Do I have any immediate plans to implement these? Sorry, but the current answer is no, I do not. Lack of development support from the public (via donations or even reviews) means that I don’t see much more happening with these free plugins other than maintenance updates to keep things compatible with newer versions of WordPress. I’m hopeful that in the future I will have more free time and the motivation to add more features to these free plugins, but for now my priority is on paid work so I can feed my family. I already spend way too much time on free support for the free plugins. More features leading to more users would just mean lots more unpaid support time that takes away from family time and other work.
As I’ve stated before, all these plugins are open source, so any one with the skills, and the time, can freely contribute or branch the plugin off to their own much more awesome version. I leave the feature requests online here partially in hopes that somebody else may be willing to donate some time to add more features.