After all the Occupy Wall Street news over the last few weeks, it may seem kind of ironic that luxury retailers have been among the top-performing stocks since the market started falling in late July. While the S&P 500 is up about 6% over the last three months (subject to extreme change almost every hour), many luxury retailers are posting strong double-digit growth. This isn't surprising -- over the last three years, many of these stocks have been triple-baggers or better.

Despite the old adage that if you have to ask how much something costs, you probably can't afford it, it's important to ask how much a stock is worth before buying it. Let's take a look at some of the top performers and see if you should add any of them to your investing wish list.

Santa Rally, slip a triple-bagger under the tree, for me

Tiffany Stock Chart

Tiffany Stock Chart by YCharts

Despite some ups and downs, owning one of the worst of these stocks, Liz Claiborne (NYSE: LIZ), would have given you high double-digit returns for the three years since the market started recovering, while the market itself delivered fairly normal results. Owning one of the best, Williams-Sonoma (NYSE: WSM), would have even come close to doubling your money every year.

Luxury retailers have been fantastic investments, and with good reason. As wealth inequality increases, retail is becoming increasingly bifurcated, with many deep-discount stores doing just as well as their luxury counterparts, while midrange brands founder.

Tiffany Revenues TTM Chart

Tiffany Revenues TTM Chart by YCharts

This doesn't necessarily mean sales have been fantastic. In fact, aside from Liz Claiborne, they haven't been much better or worse than the average of all retailers. Average sales growth for luxury retailers is still fairly impressive given the weak economy, but it doesn't explain the massive share price appreciation.

Tiffany Gross Profit Margin Chart

Tiffany Gross Profit Margin Chart by YCharts

The answers are mixed. Gross margin at Coach (NYSE: COH) barely changed, but it's hard to improve on a 72% margin. Williams-Sonoma has also done a good job of managing its inventory, carrying less as a percent of revenue, resulting in leaner operations. Oftentimes, consumers are also simply paying more per item. Generally speaking, though, luxury retailers have been insulated from the economic downturn, and investors have bid up their share price in a flight to stability.

Source: YCharts.

Also worth noting is that Liz Claiborne has improved gross margin the most, but it's safe to assume it will improve even further going forward. The company recently sold all of its mid-priced brands to J.C. Penney (NYSE: JCP) and is turning its focus toward revamping its luxury brands. The company's CEO, William McComb, intends to "re-couture" the Juicy Couture brand, fixing the minimum price of Juicy items to at least $100.

Santa Rally, I've been an awfully conservative investor
These are generally good businesses, but after returning several hundred percent in such a short period, are any of them cheap enough to buy today?

Tiffany EV / Free Cash Flow Chart

Tiffany EV / Free Cash Flow Chart by YCharts

Judging by their enterprise-value-to-free-cash-flow ratios, none of them are particularly attractive, especially Tiffany and Ralph Lauren (NYSE: RL). Williams-Sonoma's stock isn't quite as expensive as some of its merchandise, but it's still not a screaming bargain, and Liz Claiborne doesn't even register, having reported negative trailing-12-month free cash flow since the end of last year.

Just because none of these luxury stocks are bargain-priced doesn't mean they aren't worth keeping an eye on. Williams-Sonoma has improved its business a bit over the last few years, and Liz Claiborne is making some big changes to its brand portfolio, which might pay off considerably. These two are definitely worth adding to My Watchlist, the Motley Fool's wish list for investors.