Board Thread:General Discussion/@comment-11488613-20131202020552/@comment-24145588-20140507151158

Paddyokeefe wrote: On the decorations, you definitely have to weigh cost versus benefit. At the moment I've got two Grumpyres that will be making Cold Island their permanent home. Of course I'll get them a 10M Dragon Tower to rake in the cash. Dandidoo on Earth Island that's only there to make my Pompom happy? Unlikely to get a 600K Yum Yum Tree, sorry.

If you're looking at cost to benefit, then you have this one backward.

At level 15, a Grumpyre earns 294 CPM at 75% happiness, and 336 CPM at 100%. (It's the same for any 25% increase, in fact.) So, that's an additional 42 coins per minute per monster; 84 coins per minute for the two of them.

Spending 10,000,000 coins, to earn an extra 84 per minute, means you would need:

10,000,000 / 84 = 119,048 minutes = 1984 hours = 82 days, 16 hours

for your two Grumpyres to earn back what you spent on the Dragon Tower. And that's assuming you make every collection, 24/7, for the next 82 days (not very likely; if you do that sort of thing, seek professional help).

But for the Dandidoo, one of them at level 15, an extra 25% happiness yields an extra 12 CPM. Since the Yum Yum Tree costs 600,000 coins, the payback on that one is:

600,000 / 12 = 50,000 minutes = 834 hours = 34 days, 18 hours

So the one Dandidoo would pay for the Yum Yum Tree in less than half the time that the two Grumpyres would need to pay for the Dragon Tower. Although, it is true that since the Grumpyres have a higher carrying capacity, you won't lose as many coins during non-collecting times with them as you will with the Dandidoo, so once you factor in missed collections, the Dandidoo doesn't win by quite as much.

There are probably other good reasons to buy it (it looks good on your island, and 10M really isn't much money later in the game anyway), but the math doesn't support it in terms of ROI.