If at all possible, maybe we should make a planetary decision to 'spend' 500 alloys on the planet into the facilities resource pool, maybe with a short enactment time, to allow you to refill manually the resource pool.
A second option to add a planetary spirit to spend extra alloys to replenish over time could be an option, particually if you can stack the spirit and go from +5 per month to +50 in the late game when I'm earning thousands of Alloys per month seems a possible choice too.

That'll offer a choice: Long term improved spending on a fortress world on the front line, or a quick influx of alloys while you have them available to spend.