If you do overnight or long trips with 1 kid. I think a minivan is easily justified. If you plan to have more, I would start shopping after the first trimester.
It's silly how much we pack for our 2 kids driving to grandparents and such. We could not fit everything in my Accord or a small SUV. The van on the other hand can haul everything plus several more passengers and there stuff.
We haul 6 adults to a Chiefs game this past Novemeber. Cold weather gear, food, beverages, chairs, the whole set-up for Cyclone games. PLENTY of room to haul more if we needed.