It makes sense from a narrative standpoint, Vegeta has settled down and acclimatised to life on Earth, so of course he's not the same guy who tried to blow it up way back when. But I wonder if it's not also a function of the underlying patterns of his thoughts. Vegeta, much like Goku, has difficulty "fitting in", or rather, finding a way in which he can function comfortably in the society in which he finds himself living; if you are at all familiar with ASD, either as a worker or person on the spectrum, that sounds pretty damn close to home. Vegeta doesn't work. What even would he do? He can't work, not because he isn't capable in an intellectual or physical sense, but because the workplace is such an alien environment that he would be both unable to function and have little desire to do so. Vegeta is driven, not by pride, as he so often claims, but by self-actualisation; he has to get better than what he is now in order to be comfortable with himself. Not wants to, but has to. That is a very specific focus on a vary specific goal and/or idea. A possible factor of ASD so well known as to have become narrative shorthand for "intelligent and antisocial, but well-meaning". You know, the sidekick to the bland protagonist. (Oh, snap!)
Just for fun, I did a "12 Personalities" (Myers-Briggs) test answering the questions with a view to how Vegeta would answer and got the following result. I'm not going to discuss the problems with MB tests here and it doesn't necessarily fit with what I've been talking about, but it is somewhat interesting to take a look at.
Virtuosos love to explore with their hands and their eyes, touching and examining the world around them with cool rationalism and spirited curiosity. People with this personality type are natural Makers, moving from project to project, building the useful and the superfluous for the fun of it, and learning from their environment as they go. Often mechanics and engineers, Virtuosos find no greater joy than in getting their hands dirty pulling things apart and putting them back together, just a little bit better than they were before.