How about merging the quest approach (9-16, 8-16, etc.) with elements of the 3-7 evergreens (8-07 and 9-09)?
There could be a package of generic quests - The Sewer, The Old House, The Ruins, etc. These would specify the maps and a range of possible monsters and hazards, similar to 8-07 and 9-09. A GM could then assemble them into an arc consisting of 1 to 4 quests using his/her knowledge of the world of Golarion and the Pathfinder Society.
The individual quests would set the mechanical parameters of the arc, limiting the ability of GMs to make either brutal "kill them all" TPK adventures or easy walk over "speed runs." However, GMs would have a great deal of autonomy and opportunities for creativity when it comes to crafting the background, flavor, and RP elements of the scenario.
Here's a very quick and dirty example:
Happy Birthday - Drandle Dreng asks the PCs to deliver a birthday present to his noble and sainted older brother
1) The Street - random (?) thugs attempt to steal the present from the PCs
2) The Old House - Dreng's brother is missing from his house where the PCs encounter some undead and a secret door leading to the sewers
3) The Sewers - the PCs follow a trail through the sewers encountering one or more sewer critters (giant rats, gelatinous cubes, whatever) and eventually reach an exit
4) The Ruins - the PCs find Dreng's brother just as a necromancer is attempting to sacrifice him
Such a four quest arc would give 1 XP, 2 Prestige, and 500 gold to Tier 1-2 charactes similar to how quests and low-level evergreens currently work. A shorter two quest arc would provide half the rewards.
Thoughts, abuse, etc?
I adore this idea. It also gives the GMs a chance to stretch their legs, potentially, while still holding all the mechanics so they can't go too far off script!