Breeding for Cash
I was lying in bed last night going to sleep, thinking about DragonVale, as you do, and I was thinking about the Cactus Dragon ... 30 minutes for 100 000. I thought that's a pretty reasonable return on investment, started doing some sums in my head, and realised that it also earns more than Air/Sandstorm breeding, at least in the beginning. Working is below.
Cactus Dragon, 100 000 for the first hour, then 100 000 for every 30 minutes after that (as you can pop them back in the breeding cave while the next egg is hatching). So:
100 000 - 1 hour 100k/hour
300 000 - 2 hours 150k/hour
500 000 - 3 hours 166k/hour
700 000 - 4 hours 175k/hour
In the same 4 hours a Sandstorm has only earned you 500K or 125k/hour. It's a lot more labour intensive, having to check the game every 30 minutes, but if you have a peak time of 4 hours or something when you're going to be online sweeping habitats anyway, breeding Cacti Dragons is better than breeding Air/Sandstorm. However, after that point they also have the advantage of breeding again whilst the egg is hatching, so their hourly rate increases as well. Let's compare:
6 Hours
1.1 million - Cactus 183k/hour
1 million - Sandstorm 166k/hour
Still haven't caught up here, for the sake of one extra Cactus Dragon and the 100 000 it would bring. But the real interesting thing occurs at the 8 hour mark
1.5 million - Cactus 187 500/hour
1.5 million - Air/Sandstorm 187 500/hour
1.5 million - Magnetic Dragon 187 500/Hour
I find it hard to believe that's a coincidence. After that point they all continue to increase their hourly rate, but the Magnetic Dragon is increasing it by the larger amount because it is now taking advantage of "breeding whilst hatching".
12 hours
2.3 million - Cactus 191 666/hour
2.5 million - Air/Sandstorm 208 333/hour
3 million - Magnetic 250k/hour
So ... what were you thinking about in bed last night?