So you loved your L520, but now because of one thing lacking, you are trying to shift pants ?
The feature is not all that important imo. I can't say I actually miss it on my L520 at all or ever will...
Not having a flash is much worse imo, and still I don't even miss that one, cause the pics are very decent even without.
Camera Beta also fills that gap very well with its added adjustability for taking snaps.
I find that Lumia Black has much other neat things for L520 that are more usefull than glance, like double tap and sms tones.
Those I would have missed.
Sure glance is a neat little feature, but it doesn't hurt not having it, and it wouldn't have made the L520 experience any better really.
For the money I spent on this phone, this time I got more than what I bargained for, for sure !
With my previous phone, the L710, that wasn't the case. That phone really SUCKED b**ls and cost 3 times the L520.
Don't jump to conclusions because of one little detail. Weigh the pro's angainst the cons, and then make up your mind in a realistical manner.
That's all I can advise for OP...