Some quick thoughts on the initial questions posed
Do you think it's not against OOC courtesy to be exclusive in DM/Scripted quest parties of todays CoA?
A poorly worded leading question. I won't adress it. The question I will adress is: "Do you think there is a problem with OOC exclusion in DM/Scripted quests?"
The answer is No, I don't. Obviously there will be some conflict between, for example, lawful peace officials and notorious criminals, and it's perfectly fine and to be honest expected that these two won't get along well enough to go whomping dire rats together. OOC courtesy is an excelent concept to observe, but it is second to Roleplay, wich is what this server is all about. OOC courtesy is a way to let us get along as players inspiet of character conflict, it is not a carte blance excuse to break character for quests and xps and loot. Furthermore, OOC Courtesy goes both ways, if you choose to make a divisive character (like giant barbarian wereboars who literally eat peoples fingers off their hands) OOC courtesty demands you not judge someone for telling you to go away.
Should we be more inclusive in our playstyle than we currently are? Or is it just fine as it is?
CoA has an exceptionally inclusive playstyle. Top of the line as far as what my server hopping days have taught me.
Is ignoring or avoiding interaction with other characters part of a healthy PvP, and therefore good for the server?
Poorly worded and leading question. Yes, if this was a thing that actually happened it would be bad. Luckilly for us all, this is at most very rare. Some notes on this is primarilly, not all players are interested in a conflict heavy playstyle, and for these people avoiding conflict interaction is actually the Recommended Approach.
And if your character doesn't want interaction with the character, should you be OOCly exclusive as well?
I don't understand this question. If a character tells your character to sod off, that's that character telling your character to sod off. There's nothing OOC about it. No one has any obligation to include someone their characters wouldn't include. In fact, there is an expectation that you don't. You may be confusing this with OOC Courtesy, OOC Courtesy talks about how to not be a dick to people inspite of your character trying to pick a fight with theirs. It's about Respectful in Conflict, not about breaking character so people can quest and get loots easier.