economy is actually probably in the top 3 of the most important things in an mmo, probably even the most important.
nah, player-player interactions will always be #1.
I'm still thinking about Fly though. What would make not having fly ok, would be a player's ability to trade/battle over distance. So perhaps having a trading post and battling station in each P.C. could be a solution. That way people won't have to travel across regions to make a simple trade.
u can already battle without being at the same place.