I looked up how +30 weapons training would effect your DPS.
http://home.comcast.net/~amicus/Skil...%20Effects.htm
So, this means that +30 gives you 7.5% more damage. Thus 2* +30 gives you 15% more damage.
This accounts for all energy and torps/mines. But also DEM, plasma proc.
So I think this would be a good choice for (high DPS) cruisers.
And true, you have to really decide which kind of ship you wanna use with which toon for long time, because with escorts I would go for heals and +crit...