I hope I'm not derailing the thread here, but your initial post got me thinking.
Your key issue is that it is difficult to maximise the damage, to work in procs on different characters.
I can understand this - it's how i've always felt about things when i first considered multiboxing 3 70's I already had when I first started.

A lot of that is related to everything being driven from a main and not being able to micromanage watching the alt screens for these procs,
whilst healing and tanking and spamming the dps key.

What if we could come up with a way to make the handling of these damage enhancing procs much easier.
I'm thinking of perhaps the creation of an addon that you can configure on your main that alerts you to a specific proc on a specific alt.

Using your own example - hot streak procs on your mage - a message appears on your main alerting you to this, perhaps even with a distinct audio) and you hit a key that is only mapped for the mage to trigger the correct spell cast (perhaps even configurable so that it tells you what key to hit).

Is this even possible with the blizzard api - I dont know, My gut feel is that it may be possible. Perhaps I could even research how to do this.

It would require knowing when the proc occurs (may be possible as some things alert you to buffs running out)
It would require relaying that from the alt to the main
It would require the main to display that to the user.

Sorry - bit of a brain dump, something that's been sitting in the back of my mind for ages.