The goal in any regular space game is to get to communism as fast as possible. Communism unlocks state property, which is life-changing for two reasons: OPtiles and maintenance savings.
With SP, you get +1 food on workshops and watermills, which is a HUGE bonus. Grassland workshops are food-neutral, meaning with stuff like a single wet corn you can spam the BFC with them and grow to work the majority of your tiles as workshops. This production bonus cannot be overstated. As an example - until biology, each grassland farm provides +1 food, so without SP, assuming all your tiles are grassland, you would have to normally alternate 1 farm with 1 workshop to balance out the food deficit. But SP eliminates that need, meaning that now you can cover almost EVERY tile with a workshop and reap the hammer bonuses accordingly. Even plains workshops are affected, becoming only half of a food-drain as usual. So, yes, you read that right - the effect of state property on workshops
alone is to DOUBLE your hammer output in a theoretical ideal situation. Of course this ideal is often never fully reached, but coming anywhere close to it is far more powerful than any of the other economic civics have to offer in a standard game.
But we're not done with the benefits. State property also gives +1 food on watermills, as stated. The synergy of this is that watermills get progressively more powerful as the game goes on, until at electricity + RP they're +2 hammers and +3 commerce (with financial). If you slap a +1 food on that, they become the single most powerful non-resource improvement in the game,
bar none - if you thinking about it, that becomes a farm, a mine, and a hamlet
all on the same tile. So you spam riverside tiles with these, and not only do your cities grow, but they also output tremendous hammers and commerce in the process. Additionally, the +10% hammers in all cities is very welcome too, and in a game where things come down to the wire, can make a difference between winning under 250 turns and failing to do so.
However, we have yet to cover perhaps the most important aspect of SP, which is the
maintenance cost reduction. Removing distance maintenance outright is EXTREMELY powerful in large empires because, besides the obvious, from what I've observed it does two funky things. First, it makes it so that costs don't balloon progressively as a result of population. Normally, as a city grows bigger, it costs more, meaning faraway big cities will cost 20 or more gpt by the late stages of the game. Second, it caps maintenance maximum at a fixed value, which is 6gpt on monarch for however many cities you have - a paltry amount that's basically broken even by working a single 2f4h workshop by the lategame! Don't forget that colonial expenses are cancelled too.
With that in mind, our path here is clear; since we need astro anyways, we're going to reach scientific method through that, and then lib communism (lib is required for that). How do we reach SM in a timely manner, though?
Well, luckily, the paths to libbing communism are pretty bulbable by great scientists. In this particular case, I generated, which I used to knock out almost all of education and a big chunk of scientific method. That left me to self-tech just astro, philo, and lib for the most part...even with that many expenses, three techs was not a lot to get through, especially with cities coming online now and working the full extent of their riverside cottages or coastal tiles or specialists.
Only 5 turns after t150, our max beakers/turn had increased by 150:
In fact, with 25 or so cities steadily growing, AND the financial trait in play, my beakers/turn are increasing by some 20/30 every turn!
As expected, all the other AIs were cavemen (no priesthood and it's almost 1000AD,
nice 
). But I
do manage to trade for feudalism somewhere down the line, the last thing I'll ever be able to trade for before I completely shoot ahead of everyone on research.
This looks like a pretty
epic national epic spot, don't you think

?
So all of the above amounted to me reaching communism by t177. Btw, you can see in the top left/middle of the screen what improvements to make/work before state property...maximize commerce, cottage everything riverside, and especially for financial, coasts are decent.
And here, even BEFORE any of the workshop/watermill-improving techs, you can begin to see the power of state property. Notice how high my expenses are
before, and
after:
I used a great artist to start a golden age. The first image is costs and bpt before the golden age and civic switches. The second is after golden age but before civic switches...and the third is after the golden age AND switching to state property/caste system/free religion. Our base bpt already well above 1100, doubling from just 25 or so turns ago - owing to me cottagespamming riversides and cities still growing. But we also have a golden age to boot, increasing that by 40% or more for the next 12 turns at least...and the civic switch immediately saves us
250 gold per turn, not to mention boosting our actual research to over
1500 bpt. Suddenly we are casually 1-turning medieval and soon Renaissance era techs, with barely a fraction of the previous eras' expenses at 100% research. Sub-t250 space seems a lot more possible now, doesn't it

?
And, again,
this is before workshops and watermills become absolutely insane. Or Oxford, or factories/power, or most cities growing to their full potential (in fact, as you can see by the city count increasing, I haven't even finished founding cities yet - looking to settle the islands next). You haven't seen anything yet

.
A direct before/after image of the finances, just to hammer home merely the initial cost savings:
But hey, sit tight - the best is yet to come

.