Something to think about.
keep in mind that a Trade Posts primary purpose is to allow trading of resources between players.
The dividends are a secondary effect put in for 2 reasons.
1. To somewhat counter the loss of immediate capital. You have fewer resources in the short term but get a long term gain.
2. Gives the Unit a single player benefit.
And it really is a very Communal thing. any funds you put in are no longer yours, they belong and are available to everyone with trade posts. and everyone get dividends off the communal total. And honestly anytime a Player withdraws resources it will hurt every players dividends. All withdrals and re-deposits do in the long term is delay your break even point before you start to get bonus funds. but at the same time the funds are solving short term problems so i think it will balance.
It's a bit like the difference between economics and accounting. Your accountant might say that they are bad idea since you can put money in and not get any benefit in the dollar payout. but the economist says that they really are a good thing in the long term total. they help everyone involved have access to needed funds when they need it which will help the war effort in lots of small ways, the cumulative effect will be your side doing better which helps you even if not in the pocketbook.
since the compounding effect of dividends is multiplied by additional players. Its like you get a piece of everyone's pie at a pie contest, the more people, the more pie. Is it as sweet in single player? no, but at the same time you don't have other people eating your pie.
x4000 has already said he intends to amp up the payouts to make it much more lucrative. Guarantee your going to get plenty of pie and probably ice cream on it if you want.
I guarantee that he won't implement these so they end up being like Hackers in C&C generals where you just have a huge field of these thing sitting around funding all the war efforts. And I admit a field of trading posts making free money sounds nice
I must ask why you want to amass that much of a fortune? the trade posts make a large enough strategic reserve of capital to get just about anything you might need in an emergency. I think that X4000 is going to set-up a variable building cap so you can save up 320,000 of one resource. Show me a player who wants to save more then that and I'll show you a player who probably needs to spend more on sticking it to the AI.
The only reason I can figure to allow the dividends to go over the limit would be to allow the dividends get ridiculously big. which turns them into an open ended resource theoretically capable of giving you 300,000 of each resource every time they payout. I can see that breaking the game play since it essentially removes metal and crystal from being a resource you need to worry about. if you want to do that just turn on cheats and use METAL HEAD and CRYSTAL GOBLET.
It is something to consider though, and I know it will be. I had some additional suggestions to add more to these things and x4000 cautioned me to avoid over refinement and trying to get it to do too much. I just know i really am struggling to understand why you want to save so much? I don't think these things are really intended to replace Metal and Crystal collection. Supplement it nicely, but not replace it. These things do enough other things for a team that I think they are still worth it. but I don't consider them awesome enough to be a guaranteed purchase. Choices are good for games and circumstances should allow for variation in purchasing according to desired strategy and play style. If one choice is too obviously a benefit then it really ceases to be a choice at all.
But have no fear I am sure it will be considered! I know i am interested in hearing more on why you want it done that way and what you think it adds to the game play?