A typical valuation, you use a PE ratio of 10 or higher (generally accepted in the industry), with the assumption that your investment will pay off in 10+ years. I personally don't anticipate most current cryptocurrency ventures to last longer than 3 years.
I also used P/E ratio to estimate future share price, but that only works, as you say, in a recognised sector (eg Utilities) in a real world market where companies amongst other things are regulated, have access to a wide choice of capital investment, have a whole sector to base annual profit forecasts on and where they slot into the wider eco-system you could say.
Dividend Yield is a far more sensible thing to asses price on with a Bitcoin start-up especially when divs are paid weekly in this sector.
So AM-PT were operating at an annualised D/Y of approx 3:1. I've suggested ACtM will become an open and accountable enterprise once it starts trading and machines start shipping so that 3:1 could easily become 5:1 as there will be more confidence around the long-term prospects of the company. A
safe 5:1 is an exceptional annual return especially in an ever appreciating currency. That is why as BTC takes off higher through 2014 that 5:1 could become 10:1 or higher.
Now to estimate average and target share price you just need an estimate of VMC sales and ACtM farm size in relation to global hash.