Personally I don't look at the colonies themselves as far as profit/deficit goes, but if I did I'd probably see them fairly close to each other-some making 3BC, some losing 3BC-as mine tend to be relatively but of course not completely balanced. As such, looking at the domestic policy screen is all I need to determine whether I can afford to build something else.
The rest of this post is entirely more information than anyone wants or needs, and may come off as a rant (particularly against specializing planets). But that's my specialty (ooh, bad pun).
What can I say, I've done a lot of thinking about GC2's economy.
It is better to centralize money production on a few high-PQ planets. The other planets are consumers of this money. This is more effective because you can have more tax buildings as well as a higher than base population on that planet (since it has the tiles to handle it). One high-ish PQ planet can financially support 3-4 others when properly built up.
This is the theory that everyone's operating under, but assuming that all of your planets can support/do support the same population (which is obviously not necessarily always the case), it is flawed.
Obviously you'd want higher population planets to be more economic than either production or research. But in the instances that they aren't, you're better off building roughly equally. The AI's flaw is in that it funds production and research roughly equally for most of the game, and builds roughly equally as well, hence not getting the most out of its tiles. That's not our goal-our goal is to build production/economy or research/economy roughly equal.
The reasoning behind it is this: If I have two planets at 8B pop, placing a stock market on each one gives me 1.25x the first planet plus 1.25x the second planet. This is exactly equivalent to 1.25x (1st+2nd) because in this example my planets have the same income. If I were to place two stock markets on one planet, I now have 1.50x (1st) + 1.0x (2nd), which is 2.50x or 1.25x (1st+2nd)-exactly the same as in the above scenario.
The idea that you'd be better off by placing your economic structures on high quality planets is dependent on economic structures providing a compound interest increase-but they provide a simple interest increase. Going from one stock market to two increases your income from 150% to 125% (on one planet), which is a percentage increase itself of 20%, or rather 120% of the former value.
The only reasoning that you might successfully use to argue that larger planets should get more of an economic foundation is that they do in fact have more tiles to place them on, and your economy is dependent essentially on what the average value of stock markets is, which is a subset of how many there are on an absolute basis-basically, more is better.
This conflicts with both production and research as well in that each of these has a structure that grants a percentage increase. Obviously on planets where you have power plants (which are deemed useless by almost all) or resource coordination centers, or even technology or manufacturing capitals (and let's not forget the omega research center), you would want more buildings to be multiplied by your multiplier. Since TA's tech capital applies essentially as a racial bonus, and the manu cap has done so for some time, they're not quite as valuable as they should be, and in some instances you would in fact be better off by building another factory/lab, due to the factory/lab being multiplied by all other racial bonuses.
The other issue at hand is one of aggregation-research is done on an empire-wide basis, with the exception that you can only research as many techs per turn as you have owned planets (do note that this number is one higher than the stated formula for DA and TA), however this is not the case for industry. Planets build social projects and ships on an individual basis. Therefore you are theoretically better off clumping production on planets, and hence clumping economic buildings on other planets that you don't necessarily need production at.
But there's another problem-social overflow isn't truly wasted; so long as you upgrade something over it later (and the difference in cost between the new improvement and the social spent [but not money spent-which can be different thanks to bonuses] is greater than positive 50), but military overflow is wasted. Not only does it not do you any good, but you're charged for it, too. If you have a planet at 500 military production and you build a ship that costs 100 production, you're charged 500BC for it (neglecting the fact that half of a bonus is free). So it is actually unintelligent to have any more industrial production than you actually need.
Which leads us to doing a balancing act between industry and economy buildings on a planet-by-planet basis wherein we wind up having most planets be roughly balanced between enough factories to build things and enough economic buildings to run them-and the increased amount of factories allows us to build the necessary economic buildings faster, as well, leading us to a more immediate profit...or break even point.
Granted, during the colony rush, as well as at some other times in your games (like right after you build a farm on every planet), your planets will not be giving you the same income value, without accounting for stock markets. Hence it is wise to have newly colonized planets be your production/research powerhouses, and to have your older planets be your economic juggernauts-typically your homeworld. The only problem with this theory of course is that your homeworld is the only planet with a sufficient population base early enough on to colonize from, and hence requires a relatively substantial investment in production improvements to produce colony ships fast enough (however fast "fast enough" is for you).
The point at hand is that as colonies mature, you should convert them into more so economic than they are production/research (though not necessarily all-economic), but upon initial colonization they should be almost entirely either production or research, with very few economic elements.
