A wealthy man can afford anything except a conscience
-- 261st Rule of Acquisition

This strategy is best played with the Altarians, with a strong economy as primary goal and research as secondary goal.
I've chosen the following abilities:
- Max Economy bonus
- Max Morale bonus
- The rest of the points into research
- Fedaralist political party

This strategy works well on medium to large maps (I couldn't test bigger maps due to my slow computer), with common to abundant stars and habitable planets. Tight Clusters make it far easier than Scattered (more on that later).
It's also significantly easier with less enemies.
So far, I've executed this multiple times on Tough difficulty. On the highest difficulty levels however, this strategy could be difficult due to the enormous boni the AI gets.

Phase 1: The Rush

Start colonizing like crazy. Don't hesitate to rush-buy your colony ships. Research Sensors as fast as posible.
Once you got Sensors, design a new Survey vessel: One engine, one survey module and plenty life support modules.
Build about a dozen of them, they are the key to your early financial success.
After sensors, research Planetary Improvements and then the Economy line to Stock Markets.
Once you got your plenty survey ships, resume building Colony Ships.
Make a few Constructors, so you can as many mining resources as you can. Economy, Morale and Influence resources are the most important ones. In due time, make sure one of your constructors is parked next to every resource not controlled by you.
Send them everywhere, don't spare the level 1 planets, don't spare planets in your enemies' territory. Greed is a virtue!

Phase 2: Be fruitful and multiply

Put some focus into researching all the colonization techs, don't ever stop building Colony Ships until every single habitable planet is colonized.

Phase 3: Divide...

Due to the many survey vessels and your economic abilities, you should already have a fair amount of BC. As soon as you see your enemies building ships, hail them. Bribe them into pointless wars. Everyone should be at war with everyone else, leaving only yourself in total peace.
All your left-over gold should go into rush-buying wonders and trade-goods to keep for yourself.
As the war goes on, the enemy will loose its mining starbases. Quickly capture them all

Phase 4: ...and Conquer

Research all the Influence enhancing technology and some Diplomatic abilities. Keep your enemies at war.
Give weak enemies some extra money (by buying their techs and influence points), don't put much money into the stronger empires.

Soon the first planets should start flipping to you, leading to

Phase 5: Bursting the Bubble

Your own economy will explode, which is a good thing. Since you'll notice that you'll spend more and more money on supporting the weak enemies.
Likewise, your population continues to grows as more and more planets flip to you in a cataclysmic exponential cascade.

The economy of the other races will totally collapse, only your self-less donations keep them running.

Then from one week to the other, you totally stop talking to them. Soon they'll contact you and beg for help, but you pretend to be deaf. Only talk to then to refresh war treaties. Watch them stagnate.

Phase 6: The sheep with the razor-sharp claws

Research invasion technology and weapons. Your enemies should have very few planets left. Position your fleets and within a single turn, slay them all.

Victory!