But bitcoin isn't a stock, its fundamentals are different. There is no trailing P/E we could associate it with or has earnings or profit margin or anything like that.
Difficulty is a sort of fundamental, and exponential increases in difficulty support corresponding increases in price.
I won't start buying before $6.00. I would rather miss the whole thing and forget about bitcoins all together then buy above that price or EVER chase it higher. But that's just me. When/if I will start buying, I know already the whole plan, which I might fine tune as we go along, but I won't ever go outside my comfort zone. I know exactly how much I will buy, when, how much it will cost me and when I will/might sell. There isn't anyone who could influence me in a way that I would change my plan drastically. I would/will still read what people are saying but not react on it unless the price/volume tells me so. That's how I made money in the past and will do so in the future.
When bitcoin was $1 the daily trade volume (on MtGox) was around $10k USD on low days and $50k USD on strong days. By the time daily volume was above $100k+ on average, price was above $5 and on its way to $10 (volume was growing to a million).
Unless we see a massive decrease in daily trade volume from the current $500k-$1m, down to under $100k, I'd be very suprised to see prices below $5.