I ran a lot of math a while back on this system because I saw that it was broken. IMHO, the major problem with the system is one piece of flawed logic they used to create it. In the Behind the Curtain section of Epic Spells, they say that they based the seeds on the minimum level spell that fit the "typical" spell for that seed. Then, they added 10, because...well, 10 is what the D20 system is based on. This is a major flaw, as it is basically saying "Our system was designed so that if you were 5th level and wanted to cast an EPIC lightning bolt exactly the same as the real one, you'd fail 50% of the time."
Since, a lot of the spells have a LOT more power at 9th level than the minimum, once you use the Epic Spell system to increase Lightning Bolt to the power of most 9th level spells, it is too expensive.
IMO, the best way to fix this is rework the seeds, assuming the HIGHEST level spell that fits the seed. Set the minimum damage of energy to 24d6 of a meteor swarm, then don't add the +10 for no good reason. I don't have the book in front of me now, so I don't know what that would make the DC (You'd have to use the numbers for a 9th level spell instead of a 3rd), however, using this method, I found I was able to create MUCH more interesting spells that actually did something other than kill you when you cast them.
I was also directly comparing my numbers to being able to take higher level slots of using empower or energy admixture to make higher damage spells instead of Epic Spells. Reducing the DC the way I suggest is the only way to approximately even them out.
Majoru Oakheart