(So addressing his "virtues" less subtly may not do much good. It'll just make him look even louder and more annoying - or even more of a creators' pet, if we see other characters thanking him for annoying them.)
Also, the problem with calling Dillon's joie de vivre his great virtue is that it isn't unusual in the setting. When almost every character we see seems to find a lot to enjoy in life, and bounces back from setbacks within a strip or two, Dillon doesn't look special in that respect, he just looks loud about it. (Also, he's more of a whiny little pratt when he is suffering than most of the cast. And actually, the week-long crying jag after he broke up with Matt makes him look less resilient than some of the others.) I'm remembering DiDi in the front seat of Jung's car, or Gary happily playing videogames a few days after being dumped twice, just for minor examples. It's a comedy, and you can't spend dozens of strips showing characters moping, and that's great, but it makes cheerful resilience and energy the baseline, even in characters who don't act like Dillon.
And, as to him bringing Gary and Ruby out of their shells - the trouble there is that he doesn't know when to stop. Just look at all the times we see Gary looking confused at Dillon's antics, or Ruby looking downright pained and unhappy. One feels that someone could help either of them without being such an arse about it...
But he didn't with Ruby, did he? Well, he listened when she said that she was looking for a job, and spent one day providing substantial help with that, and then he dismissed all her concerns as "boring" and went back to doing whatever he wanted.Instead, he listens to Gary and Ruby's goals and says "okay, see, this is how you get there."
Heck, it crossed my mind recently that if Amber and Dillon left town right now for a three-month location shoot, leaving Ruby flat-sitting, there'd be a fifty-fifty chance that they'd come back to discover her with a job and a boyfriend. She's made her start, and she isn't stupid. She only needs so much help, but we just know that Dillon is going to give her more, and be annoying about it.
Plus, neither Gary nor Ruby ever seems to learn the lesson that they both really need from Dillon; enough assertiveness to tell him to back off and leave them in peace sometimes.
But anyway, thanks for the clarification. I now know that, any time Dillon does get hurt, I don't have to feel stupid and malicious for enjoying the sight; I can appreciate it as part of his necessary, promised character development.