Interesting stuff. Reminds me of some of the ideas I came up with to expand HeroQuest, Phoenix beat me to it by several years!
Phoenix's idea of upgrading based on completing quests is cool, and then he has gold prices for unlocking more abilities. My system gives you bonuses a lot quicker. This would work well for a dedicated gaming group that plays a lot together. With my personal system I've kept characters and passed them around (so one person might use the barbarian to upgrade him a bit, the next couple of sessions another person might use the same character a bit, etc). I assume he went over these with others too on his forum.
He spreads out the abilities over a lot more quests, granting more Mercenaries and Combat Cards are time goes on. There are plenty of quests out there of course. My goal in upgrading the Heroes was that I wanted to play through the official quests "in order" (based on what others have suggested) with the upgrades being ready to make the EQP/BQP playable with minimal need for nerfing.
In my system I used the EU as basic mercs and the NA as advanced mercs. He starts with the NA as the basic and has master mercs that have 3 body points, extra movement and the ability to gain treasure (they keep some permanently and give the rest to the nearest Hero). He lets them keep a potion too, which is cool. He didn't give them different weapons, though.
I see he put out his own custom list of cards, basically buffing out the Treasure deck, expanding the spells slightly (Ice Spells), and making the Spell scrolls available with some effort. He definitely gives an incentive to complete more quests. The Archmage idea has the Wizard lose his spell variety in favor of specialty, and I like the "solo quest" idea to upgrade him into a specialist in one Element.
Neat stuff, I'll have to read more when time permits. Anybody play using his system? I may use one or two of his ideas that I'm not using already.