Network activation question

I have a WP network setup for which is running Marketpress, Directory, Wiki amongst other plugins.

At the moment, all the plugins are activated on the main site only but I was considering creating subdomain sites for each area individually, ie. one for the Marketpress store, one of a Directory, another solely for Wiki, etc etc etc…

And here’s my question – to reduce server load I’d like to run each main plugin specifically on one site and then the main network site only to be able to pull items through to the network homepage using widgets.

Standard network activation seems to make them available on every site and doesn’t seem the most ideal way to do it, in terms of server load?!?

Can you help please?