This solution is quite complicated, but I believe it will balance dungeon wards while encouraging the farming of all paths.
First, Arenanet will need to implement speed running leaderboards for each dungeon path. These leaderboards will record the fastest path completion times for each dungeon.
After this list is in place Arenanet uses the values of these boards to balance the rewards based on completion time.
So, what evnds up happening is as certain paths get figured out and their time reduced they become less rewarding and other longer paths that need to have their time reduced become more rewarding.
In the end though the rewards of each path will be balanced against one another not against their original value. If the player base reduces the completion time of every path by 1 minute, then rewards remain the same. We want to encourage people to lower completion times.
For example, let’s say the average completion time for a dungeon path is 20 minutes. Lets assign 20 minutes a 2 gold reward, so any path that has its fastest completion time at 20 minutes will reward 2 gold. COF path 1 takes 6 minutes 30 seconds to complete.
(390 sec / 1200 sec) * 2 gold = 65 silver
The completion reward for COF path 1 is now 65 silver.
Another example would be one of the longer Arah paths. Lets say the lowest completion time on that path is 1 hour while the path average is 30 minutes.
(3600 sec / 1800 sec) * 2 gold = 4 gold
That arah path would reward 4 gold where COF 1 would reward even less than 65 silver because of the higher average completion time.
There is one final piece to the puzzle. A group that posts a first place time on the leaderboard would receive a huge reward. As would the next group to dethrone them (even if they dethrone themselves).
At length this will create an environment where the all dungeons give rewards based on their time commitment.
It would be EXTREMELY important to eliminate skips and exploits from dungeons, and I am sure many leader board resets would need to take place if a group of people break the dungeon and beat it in a fraction of the time.
The reward would not have to be gold the real idea behind this is to naturally scale rewards based on time commitment and to allow skilled players to receive better rewards by reducing the top times.