So when a planet hits Gaia I it should get a moon. The moon works a lot like a garrison (but a little bit easier to level) where it gives the whole alliance added benefit, but unlike garrisons you cannot choose which one you want you would have to work for it. Below is a quick idea on how it would work (I'm up for people to change it around to make it more balanced but i still want the worst ones first so everyone will have to work for the better stuff)

The Moon would have XV levels;
Moon.............................Nothing
Moon I...........................+5 Critical Resist
Moon II..........................+5 Splash Resist
Moon III.........................+5 Grapple Resist
Moon IV.........................+5 Stun Resist
Moon V..........................+500 Max Hull
Moon V..........................+5 Evasion
Moon VI.........................+10 Resource Capacity
Moon VII........................+10 Metal Repair
Moon VIII.......................+5 Splash Chance
Moon IX.........................+10% XP Gain
Moon X..........................-1sec Movement Speed
Moon XI.........................+10 Hit Chance
Moon XII........................+10% Damage
Moon XIII.......................+5 Critical Chance
Moon XIV......................+5% Critical Damage
Moon XV....................... Doubles Nanos (Both 24 hours and Alliance Repair)

Interesting idea.
Moon upgrades would need to be expensive, not cheap, these bonuses would presumably stack with alli perks. These additional perks would effectively set the next step in power creep. If these additional perks were 'cheap', large alli would basically immediately achieve all the perks.

Very cool idea. To avoid power creep, maybe the price of the upgrades can be scaled to the alliance size? Not sure how you can work that out though.

A moon sounds cool, especially if it has a starport. Why, this then becomes a decision for the Ali as busters can use the starport, same as defenders.

Agreed, but current suggestions far too OP IMO. Maybe reducing all bonuses by 50%, but I'm sure spellbook would look at balancing it if they were to develop this idea.
Also like the SP idea, sounds neat.

That's just it though, not everyone can achieve them. It's hard enough if your corp/alli doesn't have a planet or cluster to defend your garri, let alone doesn't have a moon. I do like the idea of the dynamics it could add to cluster attacks, but compare these bonuses to the garri bonuses and you can see that they are a lot better. Especially considering it would be an alliance wide buff. It puts more of a gap between the new people who struggle to get into a decent corp vs. those who are in established alliances.
If you take this idea, remove the fact that it's a moon and just put the stat bonuses on the planet, it removes some of the value. I think that Spellbook could add the ability to deploy a moon in a way that would 1) make it worth while deploying it and putting effort into it and 2) add more to think about when attacking/defending a cluster. Stat bonuses might be the way to go, it might be that it's a mini planet without ship capabilities, it might be that it acts similar to a SP. Whatever it is, I back the idea, the only thing I don't want to see is it making life harder for newer players.
I love the game, I have showed it to my family and friends, and they have got to level 20 and then given up because they just get ganked all the time. I think that is a problem that needs addressing, not making worse.
Maybe if these stat bonuses only apply to engagements/invies/the rift, I would consider them less OP.

If you are a new player struggling to get into a decent Corp then you wouldn't even know what the bonus's from the moon are even helping toward. This is content, this game needs more content.

I think this just advance oll alliances wich has big garrys and planets allready. makes riches to even more stronger.
And if it shoots too for defend it makes again unbalance for the busting.
we allready have garrrison perks, maybe just add them more.
That sayd, i still like the idea =) .

I don't think any of them are too overpowered apart from the nano (Moon XV) which could be changed to doubling the repairs an alliance can do or a 25% of doubling repairs.