Here's a thought I've just had: maybe the "subtext" of Xander's remark to Buffy that she isn't good at making plans that aren't battle plans wasn't (just) any resentment at her, maybe it's what he thinks about himself, that he was only someone important in the army setting (making battle plans) but will never amount to anything in this "normal life" civilian setting. Did Buffy realize that, and is that why she wasn't upset with him for saying that?
If Xander isn't making enough money on his job, that can be a catalyst for him to feel like he is stuck in a dead end job and can't be the provider he wants to be. "Will our lives get too stressful if I'm never that successful?" Last year he was in a position of authority over a lot of people and he had their respect, without the added strain of being the famous person that people were putting on the pedestal like they did with Buffy, and he seemed much happier than he is now (and happier than Buffy was at the time). He might have thought he wanted a normal life away from the fight, but he might be missing it now. His lack of superpowers didn't matter because his job was to coordinate and assign tasks to others - a Watcher-type job, as Buffy observed. Even though Xander said he didn't like being called that, his Restless
dream hinted that he would maybe like a Giles-like role. (And now in S9 Spike seems to be taking over that role again.)