mostly separate multisite content with some shared content

i've got a situation where i have one main site with multiple associated child sites.

for the most part, the child sites are essentially independent / self contained. as a result, it seems like multisite (which allows shared code base for easy drupal version upgrades and security updates) with separate dbs for the multisites (easier maintenance, backup and restore of dbs) seems like the way to go.

however, there is a need for some shared content in a one way direction from the multi sites up to the master parent site. for instance, i could see events published on the child multisites being promoted up to the main master site which would aggregate the events of the child sites and publish as teasers on the main site. i see other child content types being aggregated as teasers on the main site as well.

not sure if the promotion should be PUSHED by the multisite editors up to the parent master site or selectively PULLED by the master site editor from the children.

1) any thoughts on the best way to handle this in drupal with current modules or any thoughts on some modules that might be coming down the pipeline in d6 or d7 (or even d8)?

it seems like the domain module might do what i want but wonder how good it is in practice and from those with real world experience?

2) anybody want to say more about best method of content promotion per my PUSH / PULL analogy above?

any hints / tips / module recipes for pulling or pushing in the scenario stated above?

3) i'm wondering about the performance implications of

a) multisite with shared code base + separate multisite dbs versus
b) multisite with shared code base + shared dbs across multisites
c) separate sites altogether with own dbs / codebases (would seem to have the most configuration / optimization flexibility while making version / security upgrades and updates a lot more difficult)

any thoughts on bottlenecks based on real experience here?

thanks