Having a real reason for object decay, with space fungus and acids would just make it really cool.
I've put some thinking on the subject of material decay to save CPU and might have come up with something a bit more interesting than fungus or acid in that matter.
So, here's another idea of mine fresh out from my crazy brain.
Astilles, also known as Cracking Serpents.
The astille is a gentle giant of the void. It feature a very long, silver snake-like body ending with a very wide tail fin, a pair of long, thick and slightly curved horn, impressively large eyes and an enormous mouth armed with a tongue nearly the size of it's body. In their adult form these beasts grow to nearly 600 meters on average with recorded measures of over a kilometer, and legends of behemoths reaching over 10 kilometers.
Astilles feed from asteroids and other small bodies drifting trough space. It is an opportunist and will promptly gobble up small objects it encounter, reaching them with it's long, sticky tongue. But in vastness of space such easy meal is rare but the cracking serpent got it's ways to make itself a snack. Building up speed it ram into asteroids with it's horns to break smaller chunks off that can fit into it's mouth earning it it's nickname. An amazing footage recorded by an unsuspecting mining ship, show a feat of precision and endurance by an astille, striking a large asteroid at 45km/s turning it to pebbles, followed by 5 minutes of space-swearing from the pilot. It has a taste for iron and will most often prioritize getting to the iron rich core of asteroids discarding chunks of more valuable ores, to the pleasure of miners.
They travels trough space trough an ingenious mean. After digesting a meal the materials that weren't absorbed are directed to a holding pouch near the center of it's body, an organic tube can then quickly deliver the matter to it's tail fin that then eject it as it quickly whip back and forth. The combined speed of whipping and ejecting give astilles a weak but efficient thrust. Traveling trough space through conventional mean is a long process, thus, astilles are known to spend most of their time in an hibernation state, waking up occasionally to verify their course and avoid undesired impacts.
Their large eyes provide them with an excellent long range sight and are able to see far into the infrared wavelength. This let them detect potential food from longer distance but also recognize live ships from their heat signature. An astille never was reported to ram or eat a live ship without provocation, no matter how small. Disabled or or abandoned vessel however are at risk once they radiated enough heat.
This specie is widespread in many galaxies, nearly all the solar systems in those galaxies is host to a few astilles, rarely above 50. They reproduce asexually, and their juveniles hang on the sides of it's parent, they feed them until it become large and massive enough to break small asteroids on it's own, a process that can take a hundred year. Their numbers remain oddly stable through a system, the death of an individual appears to trigger pregnancy in another, suggesting some form of communication. They are extremely long lived, estimated to be in the millions or billions of years, or even to be immortal.
The astilles have no predator, but is often hunted for valuable resources such as it's horns or strong digestive acid. It can be unpredictable when threatened, sometime speeding away, sometime ejecting some undigested materials through it's tail at it's aggressor, but most often turning around and ramming it's aggressor once before fleeing. Nonetheless astilles are peaceful titans and does not mind ships drifting along with them. Captains of freighter and other utilitarian ships came to like their presence and always follow one if it goes in the right direction as they provide protection from pirates and bandits as well as clearing up potentially dangerous debris.
I write way too much! but shut up I'm enjoying it! not insane! i swear!
Here again, complex creature at it's core, maybe too much for what BR can accomplish. But, as crazy as they may sound, I'm thinking my creature in a game design kind of way, yet I'm trying to go away from the standard thing in games where the mobs have only one of three personality trait. 1) mindless rampage on sight with no concept of self preservation. 2) barely do anything and may or may not grasp the concept of self preservation once you shoot them. 3) the mix of the 2 others.
I believe something that does no want to or cannot interact directly with you, but affect your environment can be just as fun.
Hope you had a fun read, see you next time i dream up something half retarded. =D