Thanks to everyone for their feedback. I ended up going with Movie Studio rather than Vegas Pro for now. After giving it more thought, I think I am unlikely to need the advanced features of Vegas in the immediate future for my purposes. As an aside, I notice that the $150 upgrade link is still active on Sony’s website today, after their Oct. 31 cutoff, for anyone still sitting on the fence.
I can always upgrade to Vegas Pro at a later date if I hit any limits on Movie Studio, and the marginal cost isn’t all that high in the big scheme of things. I don’t think I will have any significant need for fire, explosions, or other effects for my home movies of the kids. If I do start down the effects path, I am thinking I might want to look at After Effects or something similar. But that’s still a ways off for me.