As mentioned my own DS211J has been flawless at hibernation and WOL. I know that if you run more apps or services you might stop the HDDs from spinning down but I've not had that personally. As I have reasonably high bit rate 1080p, some AVCHD format videos and people using mobiles for PLEX in the house I have to run a separate PLEX media server (Ubuntu) for transcoding and unfortunately it doesn't sound like the N54L could replace that. And I wouldn't look at a 'Play' model becuase it drops features and doesn't do transcoding beyond the DS app that I don't use anyway.
Because I only need to a Synology for file serving and some apps I don't need much power so a £267 DS414J or £350 DS414 would probably suffice. Not sure where you are getting your prices from
Running a N54L idle and without proper WOL/HDD hibernation isn't ideal for me so I probably just need to give this some more thought. It sounds like it might be better suited for UnRAID, FreeNAS or OMV but that's not really what I'm looking for.
As I said the new synology nas
http://forums.overclockers.co.uk/showthread.php?t=18623522 and that's the crippled one.
I think your best off staying with synology.