As the technology-heavy Nasdaq Composite Index closes in on the all-time high it reached in March 2000, investors are facing a market that barely resembles the go-go era of 15 years ago. Valuations, as measured by what investors are willing to pay for the last 12 months of earnings, are an eighth of what they were at the peak of the dot com bubble, when the Nasdaq hit an intraday record of 5,132 before falling more than 63 percent in 12 months.