Also - Trade Rights, thats awesome +66% production bonus. So it's always worth to take them, because it cuts only 25% of trade value, so in the end we gaining more income.
Oh really? -25% trade value means -25% production value too because production is based on trade value*production efficiency.
If your trade value is 10 and your production eff. is 50%, then without trade rights you get 10*0.5 = 5 ducats production income.
With trade rights you get (7.5*0.5)*1.66) = 6.22 ducats...but you're also losing 2.5 ducats of CoT value which, at 50% TE is another 1.25 ducats.
Be careful not to overstate the value of trade rights. If you're a heavy trader and have low production eff, they will actually lose you money.
If you are playing as a Merchant Republic they are great for squeezing enemy CoTs to death though, check my sig for everything you'll ever need to know about Merchant Republics.