Is buying a condominium in downtown Des Moines a good investment? When you consider the principles of macroeconomics and apply them to the theories of urban development, then factor in the current investment climate, you come up with two equally valid answers: (A) Too soon to tell; and (B) I don’t know.

Some investments seem close to being sure things. You can invest in Budweiser, for example, and hope that people never lose their fondness for mental oblivion. Probably an excellent bet.

But when you buy a downtown condo, the eventual effect on your net worth depends on what everybody else thinks. If a lot of people agree with your decision, become your neighbors and stick around, your property value should do just fine.

But not necessarily. The New York Times reported last week that “the frenzied condominium market” has collapsed in Washington, D.C., and other big cities, including Las Vegas, Miami and Boston.

“Sparse inventory has mushroomed into a glut and soaring prices have flattened out and started falling. In many cities, banks have significantly scaled back loans to condominium builders. Some have demanded that developers sell half or more of the units in a building before even beginning construction.”

You mean the pendulum swings both ways? How were we supposed to know that?

But then, Des Moines isn’t much like those places. Some people want to live in Las Vegas, whereas we’re content to live on the planet Earth. Surely our extremes won’t be as extreme as theirs.

The only way to guess how things might go in Des Moines is by looking at the past. This downtown living concept didn’t start just last year, you know. For example, The Plaza at 300 Walnut St. has been sitting at a 45-degree angle to the rest of the world for nearly two decades now. Let’s see how condo investors have done there.

According to the Polk County assessor’s Web site, 29 of The Plaza’s 183 condo units changed hands last year, all sold by existing tenants to new ones. It was an average year for sales, according to the building’s management.

Here’s a third-floor unit that sold for $150,000 in 1991. That first buyer’s investment didn’t pan out too well, because in 1996, the condo sold for $115,000. In 1998, for $116,500. By the time of the 2002 sale, downtown optimism had started to flow, and the unit sold for $130,000.

By 2006, downtown optimism had started to pool up, and the current owner paid $206,500 for 1,420 square feet and two bathrooms.

That’s not the only unit that slid down before climbing up. One third-floor condo dipped from $77,000 all the way to $60,000 before bouncing back to $115,000 in last year’s sale.

A place on the 20th floor sold for $175,000 in 1992, then plummeted like a plant knocked off the patio. It went for $145,000 in 1998, then battled back until last year it sold for — $175,000.

Up on the 23rd floor, where the views are pretty darned nice, one unit grew in value like an investment in Google. OK, nothing grows at a Google-like pace except Google, but this wasn’t bad by Central Iowa residential standards. It sold for $145,500 in 1992 and for $269,000 last spring.

From this small sampling, it looks as if downtown condos have been a decent place to put your money for the long term, but a bit unpredictable if you got restless and decided to move. Of course, that’s the past. What do these hard facts tell us about the future?

I’m going to have to go with (B).