Without seeing a picture I can't really comment on resale, but I'm thinking that I wouldn't want to look at it, nicely landscaped or not. Is it enclosed or is there open water? Do you have a link to the listing?

If by "stormwater facility" you mean an open area that is either a retention area (always has some water) or a detention area (only has water during heavy storms but is grass/natural the remainder of time), then that is dependent on buyer, but it will definitely impact value and resale.

In most situations both versions are commonly considered an amenity, so it boosts value - an HOA community insinuates that it is a landscaped area (required by it being a planned subdivision), maintained well, and probably small to mid-size parcels (e.g. 0.25-0.50acres), so having an adjacent open area that can be visually or sometimes physically used by your property is a benefit.

In some space-constrained situations these areas are designed with high retaining walls and fences, so that could become a negative depending on how it's done and it's relationship to the subdivision.

If you are just in the vicinity (your lot not backing up or adjacent) I wouldn't worry about extra mosquitos or snakes.