What you've done already looks great, but it seems like the rewards for conquering the planet are pretty weak. Foundries already largely replace the electric furnace. Maybe you could add some more rewards that play off the light-sensitivity theme, like...

• Upgraded solar panels. An especially interesting option would be to make the panels more efficient (relatively) as the solar concentration on a surface goes down. I assume that's not possible without some runtime hacking, though.
• Upgraded laser turrets and/or PLD. Would give the player an obvious goal to build towards that would help in defending against the corruption worms.
• Rearrange the tech tree so that high level laser damage and shooting speed require advancing on this planet.

And of course, to unlock this stuff, it would make sense to create some sort of demonite science pack.