Right now there's no incentive or ability to 

1)burn a Guardian (as an enemy of the Unfallen) - as despite maluses they still provide bonuses and the process takes many many turns.

2)burn a Guardian (as a friend of the Unfallen) - as bonuses for doing so are scarce  - +20 Happiness for 10 turns and take time - 5 turns to burn.

3)grow Guardians (and Guardian Guides - quest) despite Unfallen having that ability in vivo.

my proposals:

UNFALLEN and Guardians

1A.(Unfa Only)Guardians construction - construct a Guardian with luxury resources and 1 Unfallen Pops. Limit of 1 Guardian/G.Guide per planet, not counting towards general planet-limit. Luxury resources  price scales up with each Guardian on Empire.

1B.(Unfa Only) Construct Guardian Guides (after Eco reward in G&G quest) - with higher(120%) luxury resources cost, given they provide 120% base Guardian traits)and 1 Unfallen Pops. Luxury resources price scales up with each Guardian Guide on Empire.

2. (ALL)Burning a Guardian/Guardian Guide should give an ECSTATIC status for 10-20 turns on a System. 

Why this works?

1. Guardian generation provides a luxury resources sink for the Unfallen.

2. Changing a +20 Happiness to Ecstatic for 10-20 turns makes it "reasonable" to burn a gold-laying duck for short-term interest.

3. One can achieve 20 Guardians Law with patience, investment and in a reasonable amount of time, not through RNG.