Yes, she's much more apt to quip and rather inappropriately, but that can be said for most of the characters as the writing staff has clearly gone quip (and rather inappropriately) crazy. But changed overall? I'm thinking of the fact that while he watches the show (I'm sure), he already has in his mind how it's supposed to play out because he's written or read the script in all of its incarnations. Which leaves us with one glaring factor: The actor.
What if the difference that so many are noting and not appreciating can truly and mostly be lain at the door of Kristen Bell and her performance. Think of the snausage scene in Hot Dogs. I don't recall any reaction from viewers that gave Veronica a hard time for getting SO in this guy's face. Yeah, he was a jerk to Mandy, but Veronica had no business getting involved and humiliating that guy. Furthermore, she then ranted on Mandy's ass ... and again, there wasn't negative reaction to it.
I think the reason was that Bell gave undertones (and I recall discussion of it) that what Veronica was doing to snausage guy was what no one had done for her. She wasn't smug, she wasn't simpering while laying it on him. You could feel the barely repressed rage as she tore into him. This wasn't a joke. She wasn't trying to humiliate him, make light, amuse the audience. She was furious that such cockroach-like individuals were around and were giving other "nobodies" a hard time and getting laughs for it. But it wasn't about Mandy; she wasn't being selfless. It was all about Veronica and what she had been through, but we got that and understood because of the subtext and the layers of Bell's performance. And when she ragged on Mandy, it was painful and a bit cruel, but again -- it was Veronica's pain that was shining through because Veronica had taken a lot of crap too before becoming stronger. Again, we saw that because Bell layered the scene with vulnerability. We knew EXACTLY where Veronica was coming from.
However, from season two on, Bell has played Veronica as a smug, self-entitled, self-important, pretty, pretty princess. The attitude that she has brought to the role could really be the big difference in why so many now find Veronica insufferable. There is no heart. There is no vulnerability, nothing to show that when Veronica quips against people, is cruel and hurtful, it's not coming from a place of pain and anger inside of her. Veronica is above it all because that is how Bell has been playing her.
I don't deny that the writing could be helping. After all when she was cruel to the girl in season one about her father's mistress, Miss Dent called her on it and so the viewers were given that out to defend Veronica's cruelty. But again, there were scenes where we didn't get the out, but we still were on Veronica's side ... because Bell put us on Veronica's side.
I don't know. I'm not trying to cut Thomas any slack, anyone who knows me knows that I think very unhighly of him nowadays and have since Veronica's quest for "normalcy" in season two went absolutely nowhere. But, I wonder if in this, the actor is much more to blame than the creator.