But that didn't insulate them from the winds buffeting the real estate market in the months following their purchase in 2008.
After paying cash for the Mediterranean-style house with 61 feet of beach frontage, they asked San Diego County for dramatic property tax relief.
Romney, the presumptive GOP nominee for president whose wealth is estimated at $250 million, has rejected calls from Democrats and Republicans to release his income tax returns prior to 2010. But San Diego County assessor records shed light on one sliver of the couple's personal taxes during that time: a months-long effort to reduce their annual property tax bill.
Initially, the Romneys asked that their 2009 assessment, $12.24 million, be reduced to $6.8 million, maintaining that their home had lost about 45% of its value in the first seven months they owned it.
Thirteen months later, after hiring an attorney to guide them, the Romneys filed an amended appeal, contending the home had suffered a less-dramatic fall of 27.3%, to $8.9 million.
They also filed an appeal for the 2010 tax year, claiming the house had dropped further, to $7.5 million, 38.7% less than the home's assessed value.
As a result, the Romneys have saved about $109,000 in property taxes over four years.
They were far from alone in seeking a reduction. Since the real estate market crashed, about 250,000 San Diego County homes have been reassessed at lower values, sometimes at the owner's request and other times at the county's initiative.
The Romney campaign referred all questions about their La Jolla property taxes to Matthew A. Peterson, a lobbyist and attorney who helped the Romneys find the home. He has also guided them through the complex permit process for demolishing the home and rebuilding on the site.
Referring to their initial claim, Peterson said he did not know how the Romneys determined that their house value had fallen so dramatically, but he thought they may have been reacting to dismal news reports. In any case, he said, they were not required to file documentation at the beginning.
The assessor has two years to act, and while an application is pending, Peterson said, "You hire a lawyer, a team of appraisers, and you come up with a realistic value, then file a realistic appeal."
But "once I got involved," Peterson said, "the tax assessor's office was pretty darned aggressive determining the value."
Property values were dropping in La Jolla's 92037 ZIP Code, as in other places, around the time the Romneys bought into the neighborhood. World financial markets were in turmoil, and uncertainty rocked previously stable U.S. real estate.
To buttress their claims, the Romneys used La Jolla appraiser John Streb, who specializes in seven-figure homes.
Assessing a home such as the Romneys' is complicated, Streb said. There are a limited number of beachfront properties and they vary dramatically in size and quality.
The home next door to the south, at 325 Dunemere Drive, was purchased by one of Mitt Romney's best friends, Kansas City meatpacking billionaire John Miller and his wife, Victoria, for $16.5 million two months before the Romneys bought the home at 311 Dunemere.
But the Miller home is a historic property. In exchange for a dramatically lower assessment and taxes, the owners agree not to change the exterior, according to Cathy Winterrowd, principal planner for San Diego's Historical Resources Board.
Once owned by the late actor Cliff Robertson, the Miller home is assessed at only $1.74 million, according to county records, a fraction of its value. Rather than paying annual taxes of about $165,000, which one would expect for a $16.5-million home, the Millers pay $18,846.
The home on the north side of the Romneys, at 310 Dunemere, was also an unsuitable comparison, even though it had changed hands just before Streb's appraisal. Purchased as a short sale for $2.4 million in 2010, the home was quickly assessed at $4.5 million by the county, which claimed the sale price did not accurately reflect the home's market value. In that case, the property taxes nearly doubled, said the home's owner, Jeff Lepore.
Analyst Andrew LePage of the real estate metrics service DataQuick said there was no question La Jolla home prices had dropped since 2008, but that beachfront property usually holds its value better than other properties.
Working for the Romneys, Streb concluded that the entire 92037 ZIP Code had suffered a 41% decline in average sales prices between the first six months of 2008 and the six months preceding his appraisal in October 2010. He settled on a value of $7.5 million for the Romney home.
The San Diego County Assessment Appeals Board agreed that the value of the Romney home had dropped, but not by nearly as much as Streb claimed.
On Feb. 23, 2011, the board reduced the 2009 assessment by $800,000, to $11.4 million, lowering the tax bill to $125,291 from $134,909.
The 2010 assessment was reduced to $10 million, with a corresponding drop in taxes to $110,180 from $134,535.
For the 2011 tax year, the Romneys did not have to apply for a reduction, said Jeffrey Olson, division chief of assessment services for the assessor's office. The county is legally required to reassess a property automatically once it has been reduced. The county reduced the Romneys' assessment to $8.7 million. Their property tax bill for the year was $96,843 and is likely to be the same for 2012, Olson said.
From its 2009 assessed value of $12.24 million, their home has dropped 29%.
(Since purchasing their Chicago home in 2005 for $1.65 million, President Obama and his wife, Michelle, have paid annual taxes that started at about $22,000 and have risen to nearly $27,000 this year.)
Had the Romneys never applied for a reassessment, they may have received one anyway because San Diego County has taken what it calls a proactive approach to assessments after the real estate downturn.
While they could have kept fighting for a lower assessment, Peterson said, they chose not to.
"As soon as the assessor's staff came up with that number, I said, 'Well, that's significantly higher than fair market value. Do you want to proceed with a formal hearing, and they said, 'No, if that's what the assessor thinks, that's what we will go with,' " Peterson recalled.
While the low-six-figure savings may not seem like much to the Romneys, "I would think it's foolish not to request a decline in value if you are entitled," said Paul Habibi, who teaches real estate finance and development in the UCLA Anderson Graduate School of Management. "That's like saying a rich man should not bend over to pick up a hundred dollar bill."