I have some thoughts on the Cobalt Blue Lagoon. As a refresher for what it does:
The Cobalt Blue Lagoon will also be available only through the Premium line of the Event Pass. This building will produce 1 Forge Point and double the next 2 productions. However, it can only be collected 5 times. After that, it will become inactive and only provide happiness.
I really think this (and the concept it's proposing...) is going to become a lightning rod with the player community - on many levels. Suggest you take it back to the design committee and re-discuss it's value proposition and implementation concept. Furthermore, I don't believe it's in your best interests to chart a course into pure "disposal buildings" that we actually have to pay for. (See below for a possible idea to fix this, and make the idea more player community friendly/interesting...)
If you are determined to introduce buildings like that, please consider a "reasonable introduction" and make them cyclical or limited use in a timeframe, such as a week or a month. However, they should not die in 5 uses.
For example, it's clear to me that ANY single item with that short of a value cycle will not be purchased. It's unclear, but if you're trying to sweeten the Donkey enough so that you get this 2nd building for "FREE" even knowing it becomes a "boat anchor" in your city after 5 uses, then that becomes a "BOGO" concept (Buy ONE, GET ONE FREE = 2 items for 1200 diamonds).
A bit MORE palatable, but the item and concept still have a lot of room for improvement.
Here's a potential idea for you.
Let the Cobalt Blue (CBL) go out with a initial number of collection double uses higher than 5. Make it desirable, but not too "rich". Then part II of the strategy would be to create a new CBL "potion" of recharge for it. In other words, you can "reload" it with charges to make it continue to work in your city to its original goals.
Think of it like buying a RAZOR with 2 blades. You get 2 blades with your new Razor, and when they're spent, you have to buy more blade cartridges.
So then...you keep the CBL building in your city, and work to recharge it through game mechanics. Ideas could include getting the CBL potion of recharge in the daily quest, maybe GE level 4, or possibly even a special chest or incident. You can also get them in the Auction Dealer.