A few questions about planets' defense for invasions:

1) I thought I read that, when repelling an invasion, the planet's attack counts as invasion defense, but I don't remember where I read that, or if I made it up or something, so I wanted to ask if it does.

2) For structures that give "Invasion Defense", like the Lazuli Pylon, does the Legion Bonus apply to that as well? For that matter, does the Legion Bonus apply at all with regards to invasions?

Yes and Yes. You can see #1 when you mouse over the attack stat in the Planet colony tab. A planet's Attack / Defense / Invasion Defense all provide the same effect during an invasion. Legion bonuses apply at all times.

Oh, maybe that's where I read that then; I forgot it had a mouse over.

Thank you for the information. : )

Ok so do the buildings with invasion defense like the solder outpost provide the same lvl of dfence against invasions as say a planet shield once the population is down and they try to invade.....ie if my pop is gone and I am about to be invaded, I have space for a 300 point solder outpost or a 750 point planet shield is the shield better then the invasion defense or vice versa.

750 is more than 300, so the Planetary Shield is better. The only advantages of Soldier Outposts is they can't be destroyed with Crimson Cluster missiles.