Can someone summarize starbase benefits?

Starbases also help to increase your influence in the sectors that surround them (and more so if you build culture increasing modules on them).
And yes, Starbases are cumulative in their benefits, but only up to a certain point. I think that currently, with version 1.03, your total production on any planet can only go up to 3x the planets quality before any bonus's start to lose effect. So if the planet quality was 20, and you added up the military, social, and research of the planet, they could add up to 60 before incurring any penalties.

When there is no resource you can make the SB a weapon to increase the effectiveness of your fleet in it's area. The ultimate offensive level is the Death Star or whatever they call it. I use them to win cultural victory. Build them near alien planets, add the cultural upgrades and watch the screen turn blue.

I would think that usually they are (with or without resources) a key to winning. I would like to hear if anyone wins without building lots of them.

~SDC~

You can pop down a starbase and add a few defence modules where you expect the AI to attack. It will waste many ships trying to destroy the starbase, as long as you have decent repair tech the starbase will survive for a long time.

If the enemy fleet is always targetting a certain sector and has a tech advantage then place a few starbases there, add modules to increase ATT/DEF of your ships and fight the enemy only within that sector.

If the enemy is garrisoning key planets with capital ships and you can't attack effectively, then bring along a fleet of constructors and build a starbase in the enemy sector. Add ATT/DEF booster modules to increase your navy, clear out the defenders and assault the planets. Add repair modules to quickly restore your damaged ships to full hit points.

To counter enemy influence and exert influence on them, add influence modules. Once you get the Culture Palace tech this has a huge effect and can gain you hundreds of billions of new citizens. Terror Stars are IMHO over-priced and too slow, just build new Culture Palace bases instead.

If you have a sector with several good planets, build a couple of starbases and add the production-boosting modules. This will give *free* production boosts (as well as some paid-for production) on each planet in the sector. Add movement boosters to the starbases and you get a sector where you not only can build several capital ships per turn but also move them out with +10 movement - force projection at its best! Works nicely for anti-matter missiles as well

You have to choose which starbase type you want to use. It is possible to spam space with starbases, but that will be shot down in an upcoming patch I believe. Already, starbases cost 5 to maintain.
Without a resource, you can use starbases in your home sectors to boost trade and production. In border sectors, you can use them to boost trade and culture.
If you feel like you're going to be attacked somewhere, ship attack bonuses can be interesting.
I wouldn't use a starbase as a buffer against ships, since AMMs destroy starbases quite easily and are cheap. That tactic is interesting only if you have a big production advantage, in which case AMMs are probably more interesting as they destroy enemy capital ships and boost your own military rating so they are good deterrants.

The buffer starbase is really only for early game (ie before battleships). It doesn't work against capital ships and AMMs until late-game with the last few defence modules.

Regarding number of starbases and maintenance cost the key here is that there is no cost to establish a starbase (ie like the Terror Star 5000 bc cost so you can build a starbase, let it do it's (specialised) task and disband it again. Constructors are cheap on larger galaxies where you have 50-100 colonies and can't afford to churn out something that has upkeep cost.

About starbase stacking...

I usually keep one max production starbase per sector (as of V1.02), but I may build more if I want to increase...

1. Trade
2. Influence
3. Ship Attack/Defense/Speed

In the beginning, production starbases aren't worth the effort to construct. They cost 5 BC a turn and require an initial 200 BC investment (the cost of a constructor) plus 200 BC per module.

The first few production module are woefully overpriced. 400 BC plus 5 BC per turn for a 5% production increase? Even if it IS on every planet in the system, it's better to invest in social structures like Manufacturing Centers and Fusion Power Plants (or in galactic resource gathering).

Here's the way I normally see my starbases grow (based on what tech I get). I've left out Smart Drones and Orbital Replicators.

Cost/Bonus/Total Bonus/Name

400 BC - 5% - 5% - Phase I Factory
600 BC - 10% - 15% - Phase II Factory
800 BC - 5% - 20% - Interstellar Distributor I
1000 BC - 10% - 30% - Interstellar Distributor II
1200 BC - 25% - 55% - Phase III Factory
1400 BC - 15% - 70% - Interstellar Distributor III
1600 BC - 25% - 95% - Massive Scaling Center

As you can see, it's impractical to spend 800 BC on a system-wide 20% production bonus when you could spend only 150 BC per planet on a 45% increase.

- Nobody

Here is a short tutorial that I wrote:

http://cdgroup.org/forums/tbs/gc/viewtopic.php?t=94