More and better missions are all well and good, thank you for that. However, you shouldn't have to take a mission in order to find an NPC ship to fight.
Sometimes you just want to cruise around and find ships that may not be available to fight with missions. Having to only rely on missions limits the scope of the targets you can fight. It doesn't seem to me that it would take much time at all to increase the solo NPC spawn rate unless there is some CPU/RAM requirements that would cause issues. The other issue is the size of NPC fleets. With the server population on the PVE server so low its hard to find someone to group with, especially since you can only group with your own nation.
As it stands now you cant just jump into the game for an hour unless you take a mission, if a mission is available and expect to find a ship to fight. You might, but you might not be able to find a target and that limits players who maybe dont have 4 hrs to play.