The one thing I hate, when trying to complete any quest, is to have to compete for spawns. As for 1.5 I had no trouble tackling the first 3 level of encounters if the spawn was available. Since they were on a 6 hours timer, I knew that eventually they would spawn for me. I did not have the chance to kill a dragon but I took the opportunity given by some uber player to loot one. But this left me with a sour taste since I did not complete the quest by my own.
I had to resolve to take that free loot because Dragons are on 24hr spawn and I did not know if I would ever get the chance to see another one available for me.
I am not sure if it is possible, but I would replace the Dragons with either the same mob in a raid ldon or maybe use the hard ldon system that you would have to complete several times (X number of hard point) or have the final mob have a chance to drop the equivalent of the dragon heart.