It's not that I hate the L920, but the lack of customization is kinda making my fingers twitch lol. But I might get the N4 when it goes back in stock. Can anyone vouch for it's durability and battery life? Those are the two biggest things that worry me, that glass back looks fragile.
I have a 920 too, and I think you know the truth is you aren't going to find hardware half as nice as this on the Android side of the fence.
I like Android too and Jellybean seems like a huge improvement over the past versions of it. But you couldn't pay me to buy another LG phone. An LG Revolution is what actually put me off Android for almost 2 years. Horrible device with virtually non-existant support from LG. The whole experience was so wretched (my first Android phone) that I walked away from the whole platform for a while (until just recently when I bought a Nexus 7 tablet, which I like very much so far)
Anyway, I think you're on the right track...sort of. I mean, if you're going to go with Android, a Nexus device is the way to go. But LG is garbage and you're right to be wary of buying a phone with a glass backside.
If I were you, I'd stick with the 920 for a while longer. This will also give you time to really give Windows Phone 8 a fair chance. If it's ever really going to come into it's own fully, it will be this year. You should see all kinds of great apps and things rolling out for it in the upcoming months.
If you are still really itching to be able to change your UI or widgets or whatever it is that's got your fingers twitching, do it when Motorola or someone else makes the next Nexus phone. Just about anyone is better than LG. I'd give this LG one a pass. Honestly, I'd get a Galaxy Nexus before the LG, despite the difference in performance.