After purchasing all 6 expansions I feel forced to trim the adventure deck since it's not really practical to use a 350+ cards. So I am trying to decide which cards to keep and which to get rid of, my goal is to end up with a 150-160 card adventure deck.
you're free to do any alteration you wish but, as a player who felt a similar urge for adjusting the Adventure deck, I ended up putting everything together again and never think about shuffling, trimming and adapting. You might want to remove old cards to see more of the new cards, at least for the first games; then, I suggest to remove expansion-wise (remove all Reaper, all Frostmarch or all Sacred Pool cards).
If you want to remove cards for a particular purpose (e.g. you think they're lame, they drag the game, they're too good/bad), always remember that this is a card-draw game based on luck. A card is never meaningful by itself but it always depends on the circumstances when it is drawn. Realize this and you'll realize that trimming isn't really worth doing.
I have removed all enemies of Strength and Craft of 1 for start, as well as many annoying cards that no one wants to see and slow the game down such as the Ekor, Poltergeist, Leper, Centaur etc.
I don't understand why you removed these cards.
Easy Enemies are meant to give a chance to weak Characters and to be a wasted turn for stronger ones. They are an important game equalizer, especially if you don't play with big box expansions where stronger Enemies are easier to find.
The other Event/Stranger cards are annoying for the one who draws them, why do you remove them? Aren't they part of this game fun?
I have also removed all Talismans from the adventure deck because it feels cheap to find a Talisman lying around but kept alternative ways to obtain one such as the Casket, Hermit and the Tomb.
I had the same thought and I removed Talisman Adventure cards for a while, then I understood that they don't mean a thing with all the cards we have now.
1) Now what do you think of high risk/high reward cards such as the Cave or the Tomb which I mentioned above? Do you believe that they add to the game or are they just too random for players to consider encountering them?
Depends on the Character, as always. The one who draws the card doesn't have the choice, the others will decide when they have the chance to land on. Circumstances will give the answer, not speculation.
2) How about the place cards where you put 4 craft/strength/life/fate/gold tokens on them and every time a character interacts with the square can take one token, do you guys think that these are cards that make the game more interesting or do they make the game too easy since it's free stats lying around for everyone to pick up?
They're just fine, except when the Conjurer is in play.
3) Regarding the Academy card, I have been debating whether this is even worth including since spending 3 Gold and losing a turn for one point in Strength/Craft just feels too much, compared to the pool cards which I mentioned above where you put 4 tokens and can improve your stats for free. Does the Academy feel like a rewarding card or just plain tedious and slow?
It's rarely seen and used right now, but a weak Character with a lot of Gold will be happy to miss some turns there.
I will add more questions later since I would like to see what your opinions are about improving the game and what cards could be classified as "fun" and interesting compared to tedious and cards people would avoid using.
I don't want to discourage you to improve the game as you feel necessary. If you don't like some card types just remove them and see how it works. I only remind you that Talisman is a game with a low strategic profile and high random fun. It's not a Character building game, where you make choices with long-term rewards; it's a light-hearted adventure game where you have choices to do and resources to manage (better: that you mustn't forget to use), but ultimately it's not balanced, not fair to everyone, not about maximizing-minimizing what you get from the Adventure cards. You don't have control over it, period. Trimming can be done as you wish, but there are no criteria to apply besides what you like/dislike.