Maybe maybe not. Depends on if someone is doing it for fun or trying to make a profit off it.
it's more about another option for a client, maybe give someone an idea on how to improve current clients.
You could use your argument against the people running 2 6990's vs the people running 4 boxes+ of 4 6990's.
That isn't stopping people from doing 2 5830's either. See what I'm saying?
Moar options are always good and maybe it won't even be useless
No thats wrong,
If you are significant too slow it makes no Sense, that should but clear.
If it is fun to Waste Energy, Money, Calculating Time - ok that must be a rare fetish ;-)
If you are in the midfield with your hashrate (average) it is Ok,
More Speed is better but not nessessary to make Profit.
Logically the More Speed the more you get (but the Card is also more expensive...)
So my guideline is the Mhash per Watt Ratio.
My Advice 2 or more Mhash per Watt.