I love humorous and poignant stories and am glad to say Cafelit have published one of mine in each of these categories in the last few days. Consistency is a historical piece and Moving On is a changing job story, both very different in mood. I should add the mood varies for my Chandler's Ford Today pieces too. My post this week is a review of A Christmas Carol as staged by the MDG Players recently. In articles like this, as well as the actual review, I like to give some background to either the material or the writer of the material which is being performed so I generally go for an informative. chatty style. For my scam alert pieces, I obviously adopt a more serious tone.
The key, of course, is having the right "mood" for the right story or article. Yes, you can have funny crime and I've read and listened to some wonderful stories in that genre, but generally, unless it is flagged up, you would expect crime stories to have a fairly sombre tone to them. This is where the blurb on books is so important. A reader will pick up on the mood of the book and decide if it suits them thanks to that so it is vital to get this right.
With my From Light to Dark and Back Again the title is the big clue that there is a variety of moods here (as is my strapline - "a story to suit every mood").
Yes, I think you should play to your strengths when writing so if that is serious writing, go for it, but I would also say don't be afraid to experiment and play with words. If you find you can write in more than one mood or tone of story, so much the better. It will open up more competitions and markets for you to try. Good luck!