I think the implementation is fine as it is.  The logistics point cost, especially early to mid game, is enough of a strategic choice to balance the construction of these resource collectors.

I agree that the logistics cost makes the choice to build or not build interesting enough as-is.

HOWEVER, insta-build trivializes the destruction of thee resources. Thus when the SK's units ruin your metal mine, there is little consequence. You just click build again, and problem solved.

Adding a 1-2 turn build time would give you more reason to defend your resources. Outposts are already effectively invulnerable as it stands.