How about giving Eco stations repair and assist-build ability? Let Mk1's range comparible to MSD, Mk2's about half planet, and Mk3's planetary. Of course, make the ability available only at full health, so it can always recieve repairing when necessary, which is more important.
If that's not enough, how about adding planetary repair (and regen) cooldown reduction? Normal cooldown is 6 seconds, Mk1 makes it 5s, Mk2 4s, and Mk3 3s. That will make structures and ships on planet potentially much more durable.