If I have Doc and Roger blowing things up, I get people asking to see more of Pirta and Sandy.
If I have Pirta shakin' her booty, I get people asking why we haven't seen Rainy or Bandit in a while.
I put up Rainy and Bandit and I get people asking if we can see more of Jinx and Kasi.
If I have Doc & Roger in the shop, people ask when we'll see a paintball storyline.
I do a paintball storyline and people ask if I can do a story with Howie and Kasi's mom.
I do a long-format storyline like Pirta's first game, and people wonder when I'll get back to the gag-a-day.
I switch over to color- which can cost upwards of two extra hours per strip- and somebody will say they prefer the "Scraps" strips which are about ten minutes of copy-and-paste.
Now, none of that is a problem. I like getting feedback from readers, and I'm frequently amazed at how even "throwaway" characters can become instantly popular. (Kasi was originally a one-shot, and I can't even guess how many people have been asking to see more of Jake's coworker Duncan and his boss.)
I have no script, and there is no great overarching storyline I'm going by. The strip is whatever I happen to think of that day- sometimes it works, sometimes it's crap.
More than a few times I've been stuck for an idea, trying to come up with some new way for Doc and Roger to blow something up. Then I'll get an email or read a board post saying something like "When will we see Gino again?" and all of a sudden there's a good gag all laid out.
So don't be afraid to ask. I can't say I'll shoehorn your favorite character in right away, but it just might give me an idea to make a bad gag good, or a good gag better.