Bitcoins are irrelevant though, if it is dollars, or geistgeld, or icecream cones or whatever that you are after.
Heck you could look at it all from the point of view of a person who has electricity to spend instead of a person who has fiat or bitcoins or geistgeld or whatever to spend.
I have a certain amount of electricity and I want to turn it into more electricity.
I could buy a device that can mine any SHA256 coin or even merge a bunch of SHA256 coins, and use it to burn electricity to produce stuff I can sell for more electricity than I put into it.
This fixation on bitcoins ignores the versatility of the device, heck I could launch a whole new SHA256 coin to mine with the device if I thought that would buy me more electricity than mining some already existing SHA256 coin...
-MarkM-
The value of those coins are essentially zero. I know you are the merged mining champion and merged mining is the solution to all problems but it doesn't change the economics.
Currencies are fungible so anytime someone says x BTC just think of it is as BTC equivalent. If you mine 5 coins and their combined value is x BTC then it is no different than mining x BTC. If you don't like to use BTC consider the five coins as x DVC equivalent or x XYZ equivalent. It doesn't change anything.
If you spend 100 BTC on a rig that will produce <100 BTC equivalent (even including the rounding error merged mined coins) then you have a negative ROI.
It doesn't matter if your intent is to makes lots of USD or buy lots of porches with the proceeds. If you want lots of USD then 100 BTC is better than <100 BTC.
It doesn't matter if you spend USD, BTC, ounces of gold, or DVC. The unit mines produces (mainly) BTC so however you pay it has an equivalent price in BTC.
Saying I will spend 100 BTC to mine 99 or less BTC (including the value of the near worthless merged mined coins) and it doesn't matter because I only care about USD makes no sense. It doesn't matter what the future exchange rate is.
Future exchange rate drops to $10 per BTC
Hold 100 BTC = 100 * $10 = $1,000
Buy miner for 100 BTc and mine 99 BTC = 99 * $10 = $990
100 BTC is better than 99 BTC
$1,000 is better than $990
Future exchange rate drops to $1,000 per BTC
Hold 100 BTC = 100 * $1,000 = $100,000
Buy miner for 100 BTc and mine 99 BTC = 99 * $1,000 = $99,000
100 BTC is better than 99 BTC
$100,000 is better than $99,000