A grace period is a good start. I’d make it 3 months (90 days). I’m on the fence about whether it should be a one-time thing or repeatable after you lose all your structures (as it would give you time to rebuild).
I think we need to increase the price for wardecs to at least 500 million ISK - and I think this should be scalable - but in reverse, ie: if you’re wardec’ing a corporation with a lot of structures (and in theory, a larger corporation as a whole) - the price comes down by 100 million ISK per structure - to a minimum of 100 million ISK.
So if you want to go seal clubbing, it’s gonna cost you 500 million ISK to roll the dice. Target a larger corporation - the cost goes down.