I personally do not understand how GB that produce FP are so popular. Especially the one that only produces FP. (It is a different story for the GBs that also have some other benefit). The difference between GB's and other buildings (special or not), is that GB's need to be fed FPs in order to provide the benefit they do. So you invest FP, in order to get attack bonus, supply/coins bonus, goods, happiness etc. So far so good. But invest
FP in order to get back
FP, is a completely different animal. Sok, Terrace farms etc, produce FP by taking up space (and maybe people). They do not consume FP, in order to produce FP. So you are gaining FP (from day one) by building them. (And with other FP producing GB's, eg CdM or Hagia, you get attack bonus or happiness; and you get some FPs on top of that, which are of course very welcome)
And the cost in FP of leveling up a GB (especially a later age one) is huge. Yes, if you put in a fixed amount X of FP, and the building produces an amount Y of FP
per day, you will eventually get back your invested FP and start making a profit (ie gain FPs). But the 'eventually' is very far off ... I see the Cape not as an FP source, but an FP sink (I would be tempted to call it a black hole even, but that would not accurate, as you will eventually get something out of it (if you continue playing FoE long enough).
Maybe for an end game player, whose other GBs are all level 80-100, and they are sitting on hundreds of thousands of FP they have not much use of, then I guess they can throw them at the Cape (although any other GB would be better as it would provide some small benefit sooner rather than later).
I knew from an earlier calculation that it would take more than a year to get back your FP if you level Cape to level 10, and if you level it within one day (from 0 to level 10 in 1 day, so you start getting 10 fp per day from the 1st day). That is of course way too optimistic (it usually takes weeks/months), but simplifies the calculation. So reading this thread, I thought to extend the calculation for the higher levels (I knew it would get worse, as higher levels produce more FP, but you need to feed it more fp to reach each level) . But even I was amazed at how inefficient this GB is and was thinking that I must have made an error somewhere (I could not find any, but you are welcome to double-check my calculations)
Again assuming you level it in one day, and say you get it to level 50 immediately, it will take you 3.6 years to recover your investment (65,127 FP) and start gaining FP. And the higher the level, the worse it gets. So no, I do not think it is good GB for a CA player, or for any other player for that matter.
In the graphs below, the y axis is time (in days, weeks, months and years) and the x axis is the Level of Cape (always assuming you get it at that level in one go; in reality it will take weeks/months to level the Cape, so the time when you start making a profit is even further in the future).
