Re: (Nutaku) Milenium War Aigis (English Version)
Well it is a single unit combined with three fairies who we are refering to. Which yields something like 9.1k for a male gold units at 30CC20. While it may not be efficient gold wise(which I personally wouldn't want to test). I'm wondering if leveling a gold unit from 1-30 to cc then 1-20 for the combined of it and 3 fairies... would yield as much as just feeding the raw units that made that one unit.
Alright, think I follow what you're asking a bit more. I'll give an example I did recently. Just cuase I thought the higher rarity would make a larger difference then just bronze units.
As you know I've recently done combines for both of my Sybilla.
The first time I leveled the extra Sybilla to level 25. This took 6 or 7 combines of x4 DH units. When I combined this Sybilla into my other with 3 black fairies I went from lvl 60 to 67 in one go. Now just a week or two ago I got a second one which I combined into my non-cr'ed Sybilla. I used her as a level 1 with 3 black fairies. Got her to 65. So 2 levels short of my original. However I did the same 6 combines and they are even level.
The difference was that gold cost wise I did spend more on the second. However, the amount of time and effort to get the first took longer, due to having to spend Cha to get enough units and gold to do the initial combines before the final took place. The amount of gold at the highest levels was a bigger hit than at low levels but it also cost me more then a day to accomplish. With lower rairites this is going to go down in efficiency.
Simply put due to other constraints other then gold, it's just not worth leveling units up by this method. It's cost is still not "cheap", and the time due to CHA regeneration and unit cost is exponentially higher, which makes something that could be steadily done, take far longer then needed. Gold is not hard to get in the game especially since everyone does Mondays (most people skip events for Monday dailies anyways).
Another test if you want a down and dirty experiment.
Take an archer from DH. Combine one of them with 4 others from the same map. Do this 4 time units and combine to an archer from the same map. In total you will have done 4 combines and used 16 units. You then combine the last unit with those 4 you prepped. See XP gain. Now use a new Archer, and just do combines to get to the same level. It will take you less units to get there. The gold cost will also be marginal as the units themselves are over level 10.
Edit*
The short and sweet, if you have a unit under level 10, you can use units to level them so they get to 10, as it's easy and the cost is fairly minor (typically no more than two full combine).
After this due to amount of units, you will start loosing efficiency due to cost and time needed to acquire the units, as well as the resources used to acquire them.