Along the lines of this last tactic there is another tactic/bug exploitation that [MC]Hellfire suggested to me on IRC:
"i got a suggestion for the resources one.
you dont need to spend, just spend right after it ticks. and cancel just before it ticks again. that way your value will be lowered and people will think you spend your resources, while in fact you havent done a thing
It wont show as you keep them in production, so unless they scan you between x:00:00 - x:01:00 they wont know having a past in wich you actually did spend a load of resources works in these scenario's offcos"
So essentially what this tactic allows you to do is to spend your resources before your value is calculated for a given tick, this causes your value to drop significantly (which your attacker can see) but allows you to cancel the actual production without having to pay the penalty for having ships in production for a tick. This coupled with a bluff PA mail has a lot of weight.