1. Eliminate the middle track. Or provide a distinct reason for using it.
The middle track just has greater threats for no greater reward than the outer track. Therefore, most players completely ignore it. The only time they enter this section of the board is when they're on their way to the crown of command and ready to take on the endgame anyway.
As it stands, it's an extraneous bit of the game which increases the already high tedium level for no purpose whatsoever, and should be completely dispensed with.
It could be possibly reworked into something better. The outer track could be a sort of "low level character" area while the middle track could have a different monster and treasure deck making it a higher level area with higher level rewards. This could also conceivably fix some of the problems of the early game with players drawing all the high level monsters and dying all the time without any chance of progression. It would also put the most potent treasures in another deck so a player didn't have to kill some extremely weak monster and get the soul drinker sword as their reward.
2. Change the endgame drastically.
While Talisman's early game is at least an arguably fun race around the board to get experience and treasure, the endgame is an exercise in frustration.
Once again, let me summarize the endgame:
One player finally gets bored of wandering around the outer board. They get tired and decide to go for the crown of command and win the game. They do this and then must roll the die to get the other players to "submit or die". However, this never kills anyone. So, the game continues as the other players continue leveling up on the outer map for another hour or so. Finally, they decide to proceed to the crown of command and attack the initial player. The initial player now has no defense against this because they other players will have almost certainly boosted their abilities beyond his. The end result is a progression of players taking the crown of command and then losing it to the next player. The first player to the crown of command NEVER wins the game. In fact, the player who almost always wins the game is the player who drew the game out the longest and attempted the endgame after everyone else.
From what exists of the endgame, it's obviously supposed to inspire players to extreme level of conflict. I suggest turning the inner track to yet another track with a monster and treasure deck, although with no healing sorts of items and no escape. Turn the inner track into a deathmatch zone with lots of opportunities for players to land on each other and kill/steal from each other. This endgame is started whenever a player gets the requisitie items and decides to move there. Everyone is teleported to the final zone and the slaughter begins. Any character killed is out of the game at this point. The last player left standing becomes the overlord.
3. Add some kind of skill component.
Talisman has very few player interaction components. The Prophetess is the most popular character because it's one of the few elements of the game where player choice makes any difference at all. For the most part, Talisman is just rolling the d6 over and over for about 6 hours with no real player input.
I'm not sure what could really help this aspect of the game, short of scrapping it and starting over from scratch. I'm tempted to suggest more card mechanics so a player can manage his combat and movement ability more effectively. Then there would be some kind of player input as to whether they would push themselves or not. Players with better cards in their hands would eagerly face greater dangers, while players with worse cards would try playing things safe until they could improve their hand. Perhaps movement and combat could be related. Players with good combat cards would have fewer choices of movement and would have to simply accept what they ran up against. Players with bad combat cards would have greater mobility and would find it easier to evade other players and bad encounters.