U.S. stocks haven't ended their bull run. Far from it, says Byron Wien, Blackstone Advisory Partners Vice Chairman.

"I see us going to 1,500,” Wien told CNBC. “We won’t go in a straight line — it might be a saw-tooth pattern — but I think we get there by year’s end.”

The index is currently trading around 1,414.

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The U.S. economy has shown signs of improvement in recent weeks, as evidenced by stronger-than-expected retails sales, consumer-sentiment figures and industrial-production numbers.

“The U.S. is getting better,” Wien said.

Meanwhile, the European debt crisis is roiling markets less and less these days, as talk the European Central Bank may cap bond yields in government-debt auctions has relieved investors as have sentiments that European Union policymakers may give debt-ridden Greece more time to push through austerity measures.

Yields in Spanish government-bond auctions have soared as investors have demanded hefty returns for investing in the country they see as a growing default risk.

Investors, meanwhile, shouldn't fret the arrival of the so-called fiscal cliff set to strike at the end of the year.

At the end of 2012, the Bush-era tax cuts and other tax breaks are scheduled to expire while automatic cuts to public spending kick in, a one-two punch known as a "fiscal cliff" that could send the country into recession next year if left unchecked by Congress.

Lawmakers so far have been unwilling to address tax-and-spending issues in an election year though some have hinted they can return after November's elections and deal with the cliff, or even in early 2013 on a retroactive basis.

Expect lawmakers to react, as doing nothing will harm the economy — and careers.

"The fiscal cliff represents 3.8 percent of GDP – neither party will risk the political aftermath of throwing the economy into a recession," Wien said, CNBC added.

Expect to see money roll out of bond funds and into technology and cyclical stocks.

“They’ll do well enough,” Wien said.

“And consumer staples (will also attract money) – the multiples and yields are attractive, there.”

And S&P 500 level of 1,400 has been dubbed as a "rally killer" by some.

The index has soared above 1,400 before, but the level has served as a tipping point that sparked selloffs in the past, most notably during the dot.com boom over a decade ago as well as in more recent bull runs.

Still, other equity bulls advise that this time, it could be different.

"We think it's so important to recognize that it's really the valuation that matters," Goldman Sachs equity strategist Abby Joseph Cohen told CNBC.

"It's not just the price but scaling that price for the underlying earnings, underlying GDP in the economy, underlying revenue and so on, and so the valuation today at 1,400 on the S&P 500 is actually much more attractive than the prior two periods."

Others expect the rally to cool soon especially if the index sticks in a 1,415-1,425 range, said Ned Davis Research analyst Will Geisdorf, according to USA Today.

"I would eye the first break above that level with skepticism," Geisdorf informed clients in a 12-minute video, USA Today added.

"The gains will be hard to sustain."

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