it's just a stand-in for "expensive but relatable purchase". He's saying "I'm about to write so many bugs that the sum reward will be in the tens of thousands"

It's also foolish. Any true PHB has caps on bonuses linked to output that would be too low to enable a minivan.

I assume a cycle of write bug -> fix bug -> get paid until they can afford a new car!

It would have been a sports car but Wally’s not the type.

The strip came out in 1995, at the peak of the minivan boom, with around 1.3M units sold that year.