Mortgage rates are at historic lows and house prices have tumbled, but for the majority of Americans who already own homes, the best real estate deals might be in shares of professionally managed property portfolios.

The 30-year mortgage rate is near 4%, the lowest level in 40 years of records, according to Freddie Mac. Despite such cheap financing -- and a smorgasbord of government perks to lure homebuyers -- the bargains have only gotten better: The S&P/Case-Shiller Home Price Index has fallen by nearly a third over five...