Roll to Advance,Take 2

Spurred on by some discussion on Roll to Advance with Lord Kilgore, I've decided to revisit this rule variant for experience and advancement. I've already laid down why I like and dislike the proposed system, so let me go ahead and clarify my issues. Then let's see if we can't tweak the design to eliminate those problems.

1. Predictability - Gaining levels becomes too predictable. Every level, there is some X amount of adventures where there is no chance to advance. After that threshold, the variance in leveling follows a linear progression and players exactly know their chances. The opportunity to score a major haul or victory and earn a boatload of XP, thereby catapulting up the XP charts, is gone. Leveling up becomes a mechanical construct or math exercise rather than a dynamic part of the game.
2. Risk vs Reward - This is simply gone. The ability to earn XP every adventure no matter what the evening's session holds is both a benefit and detriment to emergent gameplay. While I am not trying to say that players are solely motivated by XP to play the game, the risk versus reward assessment is an integral part of the game's tactical and strategic appeal, and not just within the realm of combat. That assessment loses a vital aspect when XP is taken out of the equation. No matter what is ventured, the gain is always the same.
3. Mixed levels within a party - When you have a party of mixed levels, the AD&D advancement charts create an interesting situation. Low level characters will catch up to their higher level brethren very quickly provided they survive. So when the party overcomes a challenge and picks up 5,000XP, the mid level characters progress nicely towards their advancement and lowly Reginald the Level 1 Fighter, assuming he survives being insta-gibbed by the 6 HD monsters the party is facing down, flies into 3rd level. Roll to Advance kills this aspect of the game as well, even if the level 1 character can theoretically level up on his first adventure, he will only very slowly catch up.

So let's leave these issues up in the air for a bit and ponder some solutions. Preferably, the answers would roll elegantly into the entire system, but I think some obtuse exceptions will be necesary to fix these issues. Of course, that is entirely within the spirit of AD&D.