According to Memory Alpha we know of 15 Klingon planets, not counting Qo'Nos or Praxis.
The same site lists 3 Romulan planets, not counting Romulus and Remus.
Seeing as XI tells us that there's less than 10,000 Vulcans left out of 6 billion. It would appear that, for whatever reason, Vulcans (and Romulans) don't tend to colonize planets in large numbers.
Sorry to triple-post; I missed this one in my initial reading of the thread.
The number of mentions of planets doesn't say much, since Romulans have interacted with the Federation to a considerably less extent than the Klingons.
* Three of the five Trek series have had Klingon or half-Klingon protagonists, the Enterprise-D
made multiple visits to Qo'Nos, the Federation was deeply involved in Klingon internal affairs and fought a year-long war with the Klingons, and there have been numerous recurring Klingon characters, including Dax's old friends who were present in two series.
* The Romulans didn't interact nearly as much with the Federation. Federation-Romulan conflicts tended to be small and low key--the fight over that medical hologram-equipped ship, or the run-ins along the neutral zone--and the only Romulan characters I can think of who appeared for more than two episodes are Tomalak
and the half-human Sela. If they don't feature much in the series, why would their worlds be mentioned?