All of those concerns are completely understandable.
Voiding the warranty on a Nexus shouldn't be a problem since Google has posted factory images of the Nexus 4. If something happens and you need to do an RMA, just restore the image. There are multiple guides for this online.
A new kernel will not wipe the phone, a new ROM will, unless it is an update to an existing ROM. Like an update to CyanogenMod won't, but switching from CyanogenMod to, for example, AOKP will.
Ya camera isn't that great, totally agree. I am one of those people that rarely use a camera though. And battery life has gotten better, especially with a custom kernel.
But looking back at my post, I am guilty of something I always disliked, which was when I had a problem, nobody had any real solutions. All the "solutions" were really just workarounds. And I think that is what you need to understand about Android. You are going to have to work around the problems in order to get it working the way you want. You will need a custom launcher, a new kernel, a custom ROM, change up the lock screen, the controls, and so much more. That is typically what people do with Nexus devices.