Updated from 5:30 p.m. ET to include additional information on after-hours action. NEW YORK ( TheStreet) -- Odd day on Wall Street. The Dow Jones Industrial Average posted a solid gain as Americans shopped up a storm in March, the S&P 500 was lethargic, and the Nasdaq slumped with Apple ( AAPL) playing the role of albatross, falling for a fifth straight session. Fear not though. Tobias Levkovich, chief U.S. equity strategist at Citigroup, argued early Monday that there's good reason to believe that consumer spending will continue to hold up well despite any blips in the housing or employment data. This is because it's ultra rich who open their wallets the most, he explained. As it turns out, the ultra rich also own the majority of the stocks, so they're likely feeling awful flush these days. "Stock prices remain a key bulwark for spending potential as higher end consumers drive roughly half of discretionary spending," Levkovitch said. "While investors often focus on home prices when considering the household sector's financial health, it is critical to recognize the impact of stock prices on household wealth and thereby on retail sales trends. Furthermore, almost half of all discretionary consumer spending is coming from the top 20% of income earners who happen to own an estimated 90% of all stocks. Thus, despite the recent pullback, investors are up meaningfully from levels seen six months ago, supporting consumption." Meantime, the positives coming out of this early round of first-quarter reports were enough to prompt UBS to boost its earnings estimate for the S&P 500 on Monday. The firm went to a bottoms-up profit view of $24.50 per share, increased from $24 per share, and left intact its year-end target of 1475 for the index, which would represent a 7.7% gain from Monday's finish at 1370. From a sector standpoint, UBS sees the financials, energy and technology as the best bets to outperform. "As we look at early reports (8.7% of the S&P 500 has reported by market-cap), we see that initial results have come in very strong. In particular, earnings have exceeded forecasts by 10.4%, and revenues have beaten estimates by 2.8%," the firm noted, adding later: "Although the magnitude of earnings beats looks quite large, we are not overly surprised. More specifically, while robust economic activity and a healthy stock market pointed to strength in 1Q, consensus estimates were revised lower over the course of the quarter, contradicting these trends."