Yes, absolutely. Farms don't increase income in any way, they increase max population which leads to more income. However, they also hurt morale, making it harder to have high tax rates, and so economic buildings are always better, for adding money, then farms. Except on very high PQ planets there is no reason ever to have more then one farm, at least in my experience.

Just to clarify, there is no relation with the population of a planet and the revenue generated by Markets, Banks, Stock Markets et al?  So a planet which caps out at 8 billion will produce the same revenue as your capital at 16 billion, assuming both have the exact same number of Stock Markets? 

So would I be better off using the PQ 29 world to make a Manufacturing capital planet which can produce Massive hulled warships every other turn instead of turning it into a 24 billion population Economic capital planet?  (Which is what I've been doing to this point.)

<McCoy> "Damnit, Jim!  I'm a doctor, not an economist!  </McCoy>

From what I've read, taxes increase with the square root of your population. So double the population means 41% more income.

The advantage of high PQ planets is that they receive a morale bonus.
However a lot of players fill up low PQ planets with economic buildings, keeping the high PQ planets for research or production. Let's not forget that to get the maximum out of your manufacturing/tech capital, forges, power plants, etc. you should try to get high PQ planets dedicated solely to either production or research. So yes, if your economy can support it, I would recommend using that PQ29 planet for production.

Esp. early on pop is far more important than any econ-buildings because of the inefficiency econ-buildings do have to face when build upon lowpop planets. Further, pop itself does bring additional bonuses which are not to underestimate in any warfought game.

The (isolated) bonus pop brings to econ fades more and more once 9b people have been reached - the issue is very complex due to alot of changing factors - but generally it is to say that if your pop is below 9b it is always a good idea to let it grow.

I cannot see the problem most people have with the bad moral a highpop (econ) planet do occasionally face: Because, why even try to sustain an approval rate where people are happy? If you have 10 planets with 45% approval, but one highpop with 20% - and circumstances change and moral will drop to 12% (whatever). Who cares at all? Press turn one time - maybe 2b people die off this planet (reducing the income slightly) and moral will be restored. Economically this is much better than to lower your taxes civ-wide to just make this one planet happy.

In reality politicians will do alot to gain their votes right before an election - and, if they are going to carry out a decision which isn't generally accepted by the public, they will wait with its announcement/execution right after the election has passed. So, lowering/raising taxes to win an election actually has its counterpart in reality. Although I really can't say if this game bears any resemblance to be "realistic" at all....

One day maybe you'll try to win a warfighting suicidal game, maybe one of the tournament scenarios where the player finds himself in a difficult starting position. Then, you might find it necessary to refer to such strategies in order to survive.

This is actually why I won't play on Suicidal; I don't like the fact that it's necessary to engage in "gamey" strategies in order to compete with the AI. I'm certainly not trying to complain about anyone else's playstyle, but speaking solely for myself, if I ever reach the point that it's either Suicidal or a walkover, I'll probably just abandon the game for a while.

I will note that in my current game on Tough, it has been possible to sustain overall approval in the 70s with a tax rate of 79%. I do have two fully maximized morale resources. Income is about 200 bcs/turn factoring in huge leases from a fleet-wide upgrade and an enormous espionage budget that I don't actually need, but am operating with now as I'm at peace with everyone. So good approval and (by my standards) a strong economy aren't incompatible.