remembering back to the November run-up, and how people were suddenly turning there rigs back to bitcoin as it became much more profitable, would they have been better off mining bitcoin the whole time?
one of the main reasons I see people using for mining a altcoin is that mining bitcoin directly is no longer profitable, however, if you simply hold the mined fractions of coins, refusing to sell them for a unprofitable amount, the price will go up. calculate what price price would have to be for you to be profitable and put your sell orders there. If the hash power of the altcoins was redirected to bitcoin, the network share of others would be reduced putting pressure on them to also only sell for a higher price.
I have been wondering lately if some of the biggest miners who are making $ and BTC hand over fist are actually promoting alt coin mining and creation to keep the hashrate of bitcoin low enough that they make the largest share of the daily coins they can.
Guess I'll start. Regarding SHA-256 alts, sure the network share would be reduced. But there has been many a discussion about whether difficulty affects price (essentially, the answers have resounded a deafening no; however, because there is a new paradigm of people involved now, that ideology may have shifted). But for the most part, there are only a few strong SHA-256 alts they have good, solid, and interesting fundamentals (PPC has PoS, FRC has a deterrent to hoarding). Sure there are some copy-paste crap clones, but they don't have much of a market presence.
Additionally, a lot of the time, the arbitrage that you could make between the coins is hard to capitalize on amongst the SHA-256 coins. And with profit calculators, a lot of those coins stick around the same value so people tend to mind what is either the most profitable using a pool hopper or stick to what they like (based on various other factors).