For me, ideally there would be an additional tileset that'd replace random UFO walls with damaged versions - burnt, peppered with holes, mangled, etc, but basically staying impassable and usually blocking LOS (with armor reduced to 90, 80, in extreme cases even 50 so you can break through with a HE charge). Actual hull breaches should only happen with the "maximum fuck" weapons (I'd add Avalanche to that category, since Plasma Cannon is an end-game weapon, and nobody is using Fusion Bollocks, so, anything with 100+ damage); maybe a very small chance of a 1x1 breach with the middle-ground weapons (say, 40-99 damage).