Very good questions, but I've never gotten into the equations calculating things. I'm sure some one has. You are correct about what effects the value of trade routes and I never heard of alignment effecting it.  The one thing I can tell you that may be the cause for the sudden drop in trade value is that when you go over 10000bc/wk in income (I THINK thats net income after spending) your trade value drops by half, or something.

I thought the trade income cut was like the tax income cut, based on the size of your treasury, not income-based. Admittedly, trade is not my specialty, as it gives a truly terrible return on investment. Even at it's best, trade won't make much money except on very small maps (compared to tax income, that is).

The econ starbases failed to give you any benefit because they affect trade only when the minifreighter is in their area. If your trade route is 6 sectors long (90 spaces), each starbase will only boost the route income for a maximum of 30 out of the 180 turns the minifreighter takes to travel the route.

If you truly want to maximize income from this, specialize in short trade routes - no more than 2 or 3 sectors. Try to get multiple routes to run through the same path, then pile the starbases on in such a way that as much of the route as possible is covered at all times. If done properly, you could easily have 8 starbases covering every part of the route. Plan the route to run along a sector boundary, then line both sides with starbases.

Building the starbases is, but building just the Trade Ships alone pays off handsomely.  I built 7 Trade Ships for 85bc apiece, sent them not that far away (~5 sectors), and forgot about it.  About a year later, I discovered those routes were yielding me 450bc every turn.  Plus, the receiving civ was Friendly with me even though he was opposite alignment.

IMHO throwing on the Trade modules is worth doing if you're going to build an Economic Starbase along the route anyway, but not worth building an Economic starbase just for trade.  If all your mini-freighters spend just one turn in the zone, you recoup the cost of the 95bc constructor  (450bc * 20% = 90bc).

For that dramatic a revenue drop in one turn, though, you'd have to establish all the trade routes in one turn, or have all the mini freighters leave the starbase's influence on the same turn by some wild coincidence.

First thing, thanks to all for the helpful replies. I couldnt get on the web earlier today and was quite surprised to receive 8 answers where I had hoped for one explanation max.

I started to play GC again after about 12 years ( OS/2) of abstinence, and currently play mainly standard terranean on 'big' maps on 'hurtful'. With 8 competing races you're lucky to get an additional planet, most of the times my colony ships come back empty. This is why I regular establish trade routes: first because of the income , up to 400bc or more with effects, and even more to buy myself time against the more agressive races like drengins and yor.

Nevertheless I tend to build a more stable economy later in the game, once I have acquired additional planets. When the whole galaxy is at war, trade income normaly drops significantly, even if you research the Galactic Privateer to protect you own freigthers.

I misinterpreted the effect of starbases on trade: I always thought economic starbases would yield up to 30% trade increase irrespective of the freighters location, so I built my starbases always around my homeworld. So part of the sudden drop definitely may have occured because freighters had left this sector. 4x30% = 120% makes quite a difference in income.

I am aware though of the 10k bc barrier, nevertheless I doubt this was a factor that time. Far into the game I am constantly in financial trouble , desperately selling cheap tech to fight off bancruptcy.

And my most dreaded scenario is, when half of the galaxy suddenly and unexpectedly reach the decision that I am a threat and turn against me before I'm ready. Even races where I have good relations, dont know what triggers this effect ...

True, but sometimes it also happens out of the blue. I guess there is just some random element in it, as with the events. It just makes the game more interesting ...