U.S. stocks have been on a roll of late, with the S&P 500 hitting the latest in a series of records on Thursday, and investors expect the index's momentum to soon carry it to - if not far past - the 2,000 milestone.

The S&P is about 10 points, or 0.4 percent, from that landmark, which analysts expected would be reached toward the end of the year, according to the most recent Reuters poll. Reaching it ahead of schedule is the latest affirmation that stocks are widely preferred to bonds, even with further upside seen as limited as the Federal Reserve remains on track to end its bond-buying stimulus program in October..

The level has more psychological than fundamental significance, and it could prompt market participants to consider whether their holdings have become stretched.

The "2,000 (level) has no fundamental significance outside of suggesting that stocks are fully valued and getting more so all the time," said David Joy, chief market strategist at Ameriprise Financial in Boston. "We should see some weakness as Fed policy winds down, but I'd still rather own stocks than bonds, as in the long run they'll continue to expand."

The S&P is up 7.8 percent this year, outpacing overseas indexes and shrugging off headwinds such as a weather-depressed first quarter and political unrest abroad. Both defensive and cyclical stocks have led at times, but traders expect technology and healthcare names, the market's current leaders, to drive it over 2,000.

"Now is not the time to seek out value over growth," said Jeff Mortimer, director of investment strategy for BNY Mellon Wealth Management in Boston. "Price momentum tends to have stickiness in this kind of market."

Every S&P sector is positive year-to-date, with tech and healthcare both up about 13 percent, eclipsing the 11 percent rise of utilities, the previous leader.

Despite record levels and the lack of any sustained pullback since 2012, investors are finding reasons to buy, with U.S. stock funds getting $9.9 billion in inflows last week, according to Thomson Reuters' Lipper service.

Only two of the 27 industry groups that Wells Fargo monitors are down from 12 months ago, a breadth that leads to year-over-year gains 90 percent of the time, the firm wrote, with the S&P rising an average of 12.7 percent.

Optimism about near-term market direction hit a nine-month high in the latest AAII Sentiment Survey, with 46.1 percent of respondents expecting gains over the next six month.

"There's a good underlying tone in the market and we still have plenty of prospects for more gains," said Michael Mullaney, chief investment officer at Fiduciary Trust Co in Boston.

He added that he would not be concerned about valuation until the S&P's forward price-to-earnings ratio was 17 and its trailing P/E was 20. Those metrics currently stand at 15.7 and 17.4, respectively.