Well that will still be a nice add-on. Not to mention more features in your products will help you attract more sales. I do not have issues with having that plugin installed on all my blogs, as long as I can acheive what I am trying to.
I know it can be painful for other people to install the plugin on there blogs manually. Maybe I can help with this if you want.
I am a Web Automation Expert and know my stuff. I work with a couple of different environment, I see you are good at php and what you do, but unfortunately, my knowledge with php is a bit limited and no time to learn at this stage. If you want I can code a quick desktop application which you can freely distribute along with your plugin to help people automatically install the plugin on all their sites. I'll be happy to help where I can. I think you would have my email, you can contact me, if you want to discuss about the software.
I would really, like to see the multisite capabilities in your plugin.
Hoping to hear soon.
Praney