1. Diffusors won't help with red/blue diodes. For regular white lights there is some benefit (shop light LEDs often have "frosted" front panels for softer, more even light spread).I want to eventually place more variety of plants when I upgrade in his enclosure. Would adding something to diffuse the lights help at all?
2. From what I see, plants need way more brightness than we provide in the enclosures (general visible light, not specific blue or green spectrum). For tortoises it's fine to "flood" the enclosure with ambient light (but provide shade and hides, of course). For crepuscular species I would opt for a few spotlights over plants.