One of the main points of your post, which is the question whether good can exist without evil, has been on my mind on and off for probably more than a decade. As an atheist, I've often expressed this as the problem of evil, and I was wondering whether God could come up with an excuse. The excuses I imagined contained your own in part. Some of them are defensible, some are not. For instance, even if we accept the idea that there's no good without evil, still a person can ask "why so much evil?" For instance, when you say "Without the contrast of the undesirable aspects of existence, I fear we would be unable to find value in what we now consider to be the good times." A Jew in a concentration camp can still ask why he suffers: his question isn't a condemnation of all suffering, just a particular amount of it. And, still, his suffering could actually have been much worse!
To put it differently, the main question that the atheist asks, and that you asked initially, is: is there suffering that is inexcusable? Is there suffering that brings no benefit at all? If x type of suffering brings x type of benefit, does that mean there's no other way that benefit could be attained, except through that suffering?
What you did was take suffering as a whole, and said it's important. That's like saying bees are important. But if we put millions of bees with you in a room, they'll sting you dead. Again, to put it in philosophical parlance, the question is: is this the best of all possible worlds? Alvin Plantinga, the foremost theological philosopher, says that the Christian has no choice but to believe that's the case. If there exists the possibility of a better world, then God doesn't exist.
Anyway, a lot more could be said. I just think this topic is interesting, and you expressed it through your own thinking, and I thought I'd add some of my own philosophical perspective to it.