Prefered Game Strats

If you're talking about fun, I like to decide in advance who is going to die and in what order, and use my ninja diplomacy skills to manipulate that into happening. So, a bit like yours.

I can't say i really have a preferred strategy though - I much prefer mixing things up, aiming for a different playstyle each time (not that I always, or often, succeed trying that. )

For fun?
I like to pick a lone minor race that has a couple of targets fighting him and transfer large amounts of weapons and credits to him for free. Even building and upgrading star bases in his area then transferring it to him.
Though they normally squander the resources (I don't think the AI quite knows what to do with gifts).... it is sometimes amusing to watch

I Turtle up after the colony grab and start orchistrating AI wars.

I like to pick a lone minor race that has a couple of targets fighting him and transfer large amounts of weapons and credits to him for free. Even building and upgrading star bases in his area then transferring it to him. Though they normally squander the resources (I don't think the AI quite knows what to do with gifts).... it is sometimes amusing to watch

It's great if you give them a planet, then it unlocks thier war machine and they start steamrolling everything (especially late game).

I enjoy parking about 9 constructros in an alien system, then giving low payouts to appease them while thier colonies rebel to join me. I completly eliminated the Torians once with out even building an offenseive ship.

I often play on maps with very few planets, so sometimes I only have my homeworld and the other habitable planet in my system. If this is the case, I put all my resources into researching extremely high diplomacy levels, techs that add to my soldiering level, a vast and varied trade network, and many, many farms and trade centers. In this way, I mooch up to all the other major races, because, even though I'm a weakling with no ships, no planets, and no manufacturing cabability, they dare not attack me because of my trade and diplomacy levels. If they do make the mistake of attacking me, I get all the other civs to declare war on them, and my planets are impossible to take because of high population and soldiering levels. Plus, if I really need a tech or ship, I just buy it from the my buddies, as my treasury has been swelling the entire game from high tax rates.

Eventually, the other empires begin to love me so much that I become allies with all of them, and even if there's a holdout or two, my incredible powers of manipulation allow me to convince other civs to dispose of them. Then, all that's left is me, my allies, and a big fat alliance victory, all achieved, ideally, without ever declaring war or building a single ship.

It's great if you give them a planet, then it unlocks thier war machine and they start steamrolling everything (especially late game).

Hmm maybe that's why it's so hard to get them go offensive despite how many ships I give them.
I'll have to try that.

In the early game, I pay the top two or three AI civs to attack everyone and each other. Once my planets are protected, I go after the civs that have annoyed or slighted me. For example, in my current game, the Arceans had the nerve to threaten me with war if I didn't pay them a modest sum, twice even. Their planets are burning as we speak. After they're finished, and my massive military machine controls the majority of known space, I'll break my alliances and see who wants some.

I personally grabbed some small techs for ships and then go straight for Planetary Invasion (well, I just got the game two days ago, and I've only played three games). My first two games I tried to play diplomacy but I'm obviously a n00b at it, so I tried a military race and went straight for conquering others, and it seems effective. I must say though that I got repelled initially and felt very discouraged about that game, but I teched my ships up and crushed the Acreans (who were the most powerful at the time). After taking them over my economy boomed, so I grabbed hull upgrades and microzation (I can't remember what it is called) - but I find that one of the best techs to get for any civilization. This is purely from a military approach, I'm sure a diplomatic/economic approach is just as fun.

I'm still playing this particular game and I consider GCII one of the best strat games ever. I haven't played one this much since AOE II!

I love the influence war. I don't know why, but the way it cascades at the end is such a pleasure to watch.

The way I prefer to do it is to get a solid core of influence heavy planets, but not research any of the influence boosting techs. Then, as my borders are starting to encompass a few enemy planets, I research the influence techs in quick succession and watch those planets quickly rebel and join me. Those rebelling planets spread my influence and soon other planets are rushing to my empire.

This strat is working especially well with the 1.1 beta patch. Stardock made enemy planets rebel much more quickly than they do in 1.09X, so the cascade is really pronounced now. It's so satisfying to conquer most of the galaxy and eventually win without firing a shot.

This increased rebellion rate - will it apply to our planets as well, or only the ones the AI controls?

There's no logical reason for it to apply to AI planets only. It should apply to every planet.