There’s no question that Americans are opening their minds and wallets to small cars. But how small are most people willing to go? That’s the question I have after testing the Ford Fiesta subcompact and its kissing cousin, the Mazda2.

The Ford and Mazda hatchbacks, like the Honda Fit before them, are cute and spunky, if underpowered. But I’m still not sure I’d buy one -- especially when I could have a slightly bigger, better compact like a Mazda3 or the new-generation Ford Focus for only a bit more money.

The Fiesta, especially, can shoot right past $20,000. Come spring, you’ll be able to own a smartly equipped Focus –- with more style, space, power and handling -- for maybe $1,000 to $2,000 more. And while Ford has touted the Fiesta’s 40-mpg highway fuel economy, I didn’t come close to that during my testing, achieving closer to 35 mpg –- identical to the mileage I’ve seen in the larger Focus or Honda Civic.

In cities such as San Francisco, or in my parking-challenged Brooklyn neighborhood, city cars like the Ford, Mazda and MINI make the most sense. They’re the kind of pee-wees that I think will barely squeeze into a space, and when I jump out, I still have 3 feet behind my rear bumper. But you know what? I’ve never had a problem parking a conventional compact here, either. In any American city, metered spaces or mall slots are big enough to handle even huge SUVs, so no advantage there. And radical downsizing seems even more dubious in the Midwestern suburbs or pickup-loving Texas, where driveway and parking space isn’t at a premium.

According to J.D. Power and Associates, subcompacts have grabbed a record 3.8 percent of the market so far in 2010, up from barely 1 percent five years ago. Power projects that subcompacts’ market share will break 5 percent in 2013, but then hold flat through 2017. In other words, growth will peak. Subcompacts will be miles better than before, but they’re still for a relatively select audience. And the big reason, of course, is that Americans have no incentive to radically downsize, unless and until gas prices shoot to $5 per gallon or more.

Certainly, groundbreaking cars like the MINI and soon the Fiat 500 have popularized the segment. More Americans are discovering the joys of hot-handling, fuel-sipping, European-style cars like the Volkswagen GTI. I’ve owned two GTIs in my life, and like any hot-hatch fanatic, I’ve spent years convincing skeptics how rewarding they can be to drive. But America isn't Europe, where gasoline costs roughly $6 per gallon and where owners are heavily taxed for driving gasoline cars -- as opposed to government-favored diesels -- and especially gas cars with large-displacement engines. Throw in narrow streets and congested cities from London to Rome, and you can see why minicars are popular there.

This spring’s arrival of the European-market Focus, one of the world’s best compacts, will be an acid test, one that may yet burn the new Fiesta. For most Americans, a Focus-sized machine is what you visualize when you think “small car.” Without the prospect of saving serious money on price or gasoline, there may be little reason to go smaller.