I take it from your post this is your first experience with any sort of virtual tabletop. "4 hours" of prep time for an hour or two of play time is pretty much the norm. This goes all the way back to the Neverwinter Nights era 10 years ago who first attempted this VTT thing.
They did a pretty good job of it but what you are saying is right, it is a HUGE time commitment. Most people will just wait for the dedicated few to do most of the content building like NWN ended up being too. But you are also correct that right now the GM client is waaaay too limited for a fully realized Virtual Tabletop. I like to think now that they've released some resources can be dedicated into turning this thing awesome.
The game will only have true longevity around this gameplay mode if we are being honest. 4 players, and some of the limitations you mentioned will cause this thing to die on the vine, but given how early it is I'm still hopeful they kick this into high gear. There is -definitely- a market for it and has been for a good while.
