Grinding Dragon Shards

So you may have gotten quite far with your dragon development only to realize the immense cost it suddenly requires to develop your dragon's skills from say 8 to 9 or 9 to 10. Now you may have been a bit loosely grinding different levels of dragons throughout your progress, but I am here to tell you you shouldnt be. There is a significant increase in the cost of resources as well as the total AP required the higher level of Gnome Boss you wish to take down. 

Say you are in a similar position like myself, with 292k Strongest Troop Power (STP), I can only guaranteed kill a level 9 gnome boss in 1 attempt. With level 10 to 12, I need 2 attempts, doubling the AP consumption. For level 13-15 I need 3 attempts. 

Now if we estimate the average AP consumtion needed is 95, its either [95], [190] or [285] Ap needed for a dragon chest. In a scenario where we truly wish to grind we can actually put a price on AP costing 100 gems per 500. It's here by costing us either [19], [38] or [47] gems per dragon chest. 

AP Cost

On top of the cost of AP there is also a significant difference in the troop loses for higher level Gnome Bosses. Once again, taking my march as an example I have the following deaths for the Lightning Gnome Boss: 

Level 9: 817

Level 10: 1648

Level 11: 3424

Level 12: 4339

Level 13: 4717

Level 14: 6508

Level 15: 7802

Resource Cost (Wishing Fountain)

Now to calculate the cost of above, i'm gonna use the wishing fountain as a mean of resource acqusation. In my case, I always go to level 30, but very rarely above. What this means in my example is that these are resources available to me everyday for a fixed price. So not a special event price or similar. 

The cost goes like this: 

We can now put a price on all our lost troops and translate them into gem cost, by multiplying our gems per resources by the number of deaths. 

We get the following gem costs: 

Level 9: 67

Level 10: 136

Level 11: 282

Level 12: 357

Level 13: 388

Level 14: 535

Level 15: 642

Instant Chest Cost

Now finally, the idea here is to evaluate the cost of speeding through our dragon chests and rapidly gain progress, so we are gonna rush some chests. They each have a cost and if we estimate reward from blue chests and the quick unlock cost of 340 minus 10% from the talent - DO NOT FORGET TO PUT THIS TALENT ON - we have a base of 306 gems per chest, with the following rewards: 

So in conclusion if you are to rush through several chests and hereby need to spend gems on AP, troop recovery and opening chests, lower level dragons are the most effecient way to go about it.