A couple of other things you didn’t mention:
a. even if we sucessfully breed a “superplant” that has no undesirable characteristics and all the highly desirable ones, since genes easily mutate and recombine, would it stay the way we want it for very long?
b. nearly all crops are pollinated by insects or wind. Crops that are now organic won’t stay that way for long. GM pollen is bound to get mixed with organic pollen, and then you may get “Frankenplant” or something you weren’t expecting and don’t want.
c. There are bound to be GM plants developed with very undesirable characteristics that may even get loose and breed on their own. Be careful what you wish for–you just may get it. For all the promise the genetic modification seems to have, it may turn out to be a Pandora’s Box. There have even been newspaper articles within the last two years about how people can do their owm genetic manipulation at home in the kitchen. If this is actually possible, this scares the bejeebers out of me. Some people may actually try to create harmful organisms. I have no doubt that rogue nations and many of our world neighbors are doing just that.