My feelings on Guardians are that most of them don't serve much purpose. If you replaced each guardian spawn with a similar power level of fleet ships I don't think anyone would notice the difference. If you make them weak then they're ignorable. If you make them extremely strong then they're problematic, but you deal with them just like you would deal with more fleet ships, bring more guns. If they have extremely powerful effects, e.g. the EMP guardian, then they can end up being extremely frustrating. The EMP specifically can punish you for not reading the corner of the screen or having the volume turned off.
So a change to guardians should:
1) Make them a challenge such that they are not ignorable or trivially solvable (run the fleetball into them).
2) Make them so that the danger they pose are within player control, but are not do-or-die frustrating (EMPs, some combination of guardian/shield/guardpost that is massively time consuming).
My proposal:
Make guardians big and mean for their matk. Give them a big shield, really slow engines, and some long range guns. Have guardians activate the same way they do now, or in reaction to a certain amount of player FP in the system. When a guardian activates, disable their shield, weapons, engines etc, start a timer of some moderate length. When the timer hits zero have them jump 2x their mark level in systems toward the nearest human homeworld, activate their shields and start chugging toward it.
Why I am in favor of this idea:
1) Guardians are a challenge that MUST be addressed when taking a system, and the player's choices have consequence. If you leave them be while you take out the ships and guardposts attacking you then you will have to deal with their deepstrike. If you decide to take them out while they are helpless, you may have to make sub-optimal decisions such as charging a guardpost that gets good multipliers against your ships so you can blow up the guardian before it warps out. If you decide to mix it up, you get to choose which guardians you will go after while helpless and which you let activate. In short, guardians give players a lot of options on how they want to play, and it allows players to take advantage of their tech/ship unlocks and their general strategy as they like.
2) A new mechanic could allow for more balancing without just tweaking numbers. For example, logicstics stations could cause guardians to "spend" extra jumps to pass through them. A new AI type may exclusively use guardians that deepstrike further. Alarm Guardposts would be something to REALLY play around.
Any thoughts?