Your email is very timely as I've been considering a few of these issues while looking at the submissions for the Dashlet Challenge.
Regarding the packaging, I myself always try to package up both the Share and repository customisations into a single JAR.
Normally this JAR can be placed in Tomcat's shared/classes directory, although sometimes it is necessary to place it inside each webapp, for instance if it contains Java classes.
I believe all the add-ons on Share Extras today use a single JAR like this, and this would be my preference since it makes installation much easier.
The add-on itself sounds interesting, although I would want to take a deeper look at it to see what value it adds for Enterprise installations as you mention similar functionality is already included there.
On the matter of contribution, of course we welcome suitable contributions provided that the Share Extras project is used for managing the source code, downloads and documentation. There is more information on some of the more detailed requirements such as licensing on the Contribution page on the Share Extras wiki, which also talks about packaging.
Thanks for taking the time to let us know about the add-on. You should find the information I mentioned helpful, and there are also many examples of combined Share/repository customisations on the site (the Site Poll in particular springs to mind).
Please do reply back if you have any further thoughts on what I've mentioned here, or let us know how you get on with the packaging etc or if you have any further questions.
Sent from my iPhone