I just saw my psychiatrist. She didn't thing trying Wellbutrin was a bad idea. She looked up some side effects--she saw that seizures were a possibility, but I don't have any of the high risk factors (alcohol use was one, but I don't drink anymore!
).
She suggested I just try adding on the Wellbutrin first, to see how my mind and body respond to it. If all goes well, the we'll wean off the Effexor.
Thanks for all your responses, guys!