Stupid question - do I need an EVSE?

Is an EVSE necessary to communicate with the car and get it to charge, or is it possible to simply feed 240v @ 20A to a J1772 cord and plug it in?

No.
The EVSE is basically a safety device. It has Ground Fault Interruption function. There is no voltage at the J1772 until there is a 'Hand Shake' with the car. Then the relay closes. It's on or off internally.
And it does establish a communication to tell the car how much current the car's On Board Charger can draw. (3.3kW for the Spark EV)

You don't want to be Griswold's Brother-in-Law standing out in the rain with a live 240 V extension cord in one hand and a beer in the other.

If that's all an EVSE does, why are they so damn expensive?!!?

Well, there's about $125 worth of cord and connectors, a 30A A/C contactor is about $25, plus you need a rudimentary brain, a toroid coil for ground fault sensing, and a housing to put it all in.

I found some nice looking portable 16A units on Amazon and Ebay for about $280-300, under the name Duosida.
Then I found the same on Alibaba for as little as $130 plus freight.

Oh, well, if Bosch wants to give me one, then that's what I'll do, provided that GM wants to give me a car first. I'm not paying $140 a month for it, it has to be two digits before I'll dive in.