I like the weathering, but heres a really good tip:
Try to keep silvered weathering on corners and edges where paint will get scraped off, not on smoott (especially rescessed) surfaces, which should have black dirt and grime because its a hard spot to clean, and the plasma burns are best scratchbuilt and added to the pep to give them a good deep recess, though there are a few types of damage to do:
-Craters, usually very circular, all black as if it has been burned.
-Punctures, like a rifle round or spiker spike that didnt quite penetrate, which should be indented around the hole, and silvered, not to mention shaped like whatever impacted it, say, a deep energy sword glancing blow, or even an indent from the can opener on the grav hammer.
-Then you have the less common, melting or corrosion, good for a spartan thats been fighting the flood, or is a zombie.
With these weathering techniques you will have a photo-realistic piece.
Also I reccomend making a stencil with a ruler and exacto, if you want clean looking print.