I've found hash rate is a good indicator for difficulty but I wouldn't agree it affects the price that much, the reason being is when you get price spikes all the short sighted multi-pools switch to that particular coin, I find difficulty is a more reliable thing and of course how many coins are in circulation.
For alts yes, for Bitcoin no. People spending thousands on ASICs might dabble in ALTs, but I think most will be pretty constantly be mining BTC to try to get ROI.