No it wouldn't make electric vehicles more economic. It takes many orders of magnitude more energy (and thus money) to create and capture antimatter than we'd ever get out of it in your car.
Right now it takes many orders of magnitude more energy.
When electricity was first being invented for human utility, I bet it took several orders of magnitude more energy to package it than to simply light a candle, for example.
Or when candles were first invented, it took several orders of magnitude more energy to create one than to keep a campfire going. Etc.
Right now we're at the "invent a candle" stage, and talking about the "hydroelectric dam" stage, so it's hard to imagine. But it's far from impossible.
