Cheers Rodders. The short-term answer is "no".
Firstly, and most importantly, I feel that two trilogies (and a few short stories) is a decent amount of work, and I feel that the quality of the books has been pretty consistent throughout. Everyone can think of a comedy series that went on too long, or that turned into a soap opera instead of a way of delivering laughs. I really don't want to go that way. (Also, of course, the main arc of the plot is more or less over.)
Secondly, I find it hard to write comedy these days. I can't go into much detail here, but I have seen little that makes me proud or fond of the UK and, particularly, England, in the last few years. Every country contains both bad and good in its nature, and at the moment, the bad vastly outweighs the good. In my current writing, I keep turning to Theoden's question, "What can men do against such reckless hate?", which is an important one, but not something I can be funny about.
However, that isn't to say that I never will. I do feel the urge to write humorously, and I've greatly enjoyed doing the Smith books. I wonder if a spin-off would be a good idea: perhaps less of a war story than a spy novel, and a comedy-drama instead of a straight comedy. We will see. At present, I am working on a series of long fantasy novels, which I am determined to finish. Once that project is over - perhaps in Autumn this year - I will give Smith's world another look.
Sorry not to be more definite!