The summer of 2007 stood out as a time of frothy acquisitions for buyout firms. But among all the mega-deals being done, the sale that year of mid-sized retailer Spencer Spirit Holdings Inc to a U.S.-based fund of ACON Investments LLC didn’t attract much attention.

ACON Investments stepped up to buy one operating company with two separate store chains for what it considered an attractive multiple after spotting more growth potential than other bidders did. ACON Investments paid 4.12x EBITDA, much less than the public comparable ...