I prefer to fight the monsters regardless of whether I get exp and loot for them or not.  Combat is fun.  

That’s why I give XP for everything they do. If they stop and help a carter with a wagon stuck in a rut, they get XP for it. That way, the only deciding factor is what did the Players choose for their PCs to do. Much simpler.

Good input all around. Needed the same advice. Been going on a scaled system, encounter based. Works ok but it lacks the reward feeling for those extra good ideas. But that's what inspiration die are also for

I've not trawled through the whole thread so this may have been addressed.

For keeping the bad guys in line with the adventurers (IE not leveling the players up faster than the plot progresses), it's worth having some key bad-guy accomplishments planned out which you can implement in the background whilst the players are leveling up - EG, to take lord of the rings as a good one which people will know the story of;

level 1 - start
level 3 - the BBEG has knowledge of the heroes
level 5 - the BBEG has recruited Saruman to his side
level 7 - Saruman has raised an army
level 9 - Saruman has marched on Minas Tirith
etc.

So as the players level up, you progress things which hte players haven't interfered with - perhaps it's replacing more people in town with doppelgangers, or a dragon starts to wake up and steal livestock to eat in the night (liking the drama that it causes amongst the peasants). This will bring things to a head where the players feel they have to do something or the enemy will win, rather than "if we just go into the forest and kill boars for a few months, we can get the levels we need to kill the BBEG!"