running a high circle (level, tier etc) campaign is the same all the times.
if you have build great foundations, you can still manage the campaing, ED has VERY good high tier opponents:
1) other adepts
2) horrors
3) dragons
4) the game of politics and diplomacy
i think is more a matter of having the same game played for 3 years that probably will bore the group;
dont forget that time goes on, and maybe other games pops out, or just RL kicks in and changes the situation of the party and such
reading that group history, it was pretty involved in GREAT affairs before having the right level probably
or who knows
but ED is really balanced for a game that involves many high circle adepts
you just have to know how to handle that game, so it falls more on the shoulders of the GM to remain interesting, challenging and fun than in the game by itself
in my 18 months old campaign, the players are above 5 and under 6, i have already layered some foundation for a game that can goes on for at least 2 full years.
but 2 of my 4 players are a married couple trying to get a baby and if they can do that, i think that my uber nice fun and interesting campaign will crumble

another thing is that the majority of the GM around are basically good geared to GM a low level circle (because we all start from circle 1) while there is a relatively low experience in dealing with high circles campaigns (or level or whatever).