1) Once you've upgraded your level to level 12 it is difficult to progress individual attributes (strength etc) as you can't cash in trophies. This slows down your progress dramatically.
2) You need a fairly rounded character strong in all areas to progress the Inner Region as you are challenged on Strength, Willpower and Cunning, so you need to strengthen every attribute - no taking daring chances to the middle as a strategy.
3) Power cards (spells?) play an overpowering role in the game compared to Influence (gold?). Any characters without power cards are unlikely to progress the game well - unlike in Talisman where there are strong non-magic characters and gold-based characters.
Overall, the upgrade mechanism tries to bring all characters to upgrade their attributed in a more rounded manner making the gameplay of most characters to be much more similar than in Talisman.
Now, these are my opinions and my opinions only. I play Relic about once a month and Talisman about once a month. So I am getting a pretty good picture of player progress. Some of these games are with 2 3 or 4 players.
In Relic, you really don't need to level up to 12 to travel to the middle. In fact, I would advise not to. It takes too long. Someone will have a go at the center by 7-8 because by level 8 you automatically move 1 more space when you enter the inner tier.
You don't need a fairly rounded character either. In my many plays, I find rounded characters to be annoyingly slow and difficult to upgrade. With a Strength based character, I try to land on a red square most of the time and I will likely be increasing my strength rapidly through level upgrades. So what if I suck at willpower? I will loose a life in the inner tier, but if I have enough lives, I can soak it up very easily.
When I play the sister of battle, my favorite character, I choose 2 attributes to increase and let the third one untouched. That to me, is a great tactic for Relic. Choose 2 attributes, let the third one, your weakest, remain the weakest and focus on 2.
You want two strong attributes because you want some flexibility when it comes to fighting. One attribute is too narrow and it will be difficult to always land on the spaces you want. Three attributes is too many and your progress will be quite slow, Besides, very few characters give you the opportunity to upgrade all 3 attributes. I feel 2 is the right number.
Power cards can become silly, especially with powerful relic interactions: the one that gives you a 6 all the times for example. But I agree that power cards are far more useful than Talisman spells, and I love, love, love the fact that you can use it as a dice roll. For your movement, this is unbelievably critical. You have a strong willpower and a blue tyranid enemy worth 6 pts is waiting face up 3 squares away and you have a Power Card of 3 in your player area. Forget the dice, use the power card to immediately travel there, kill the bug and earn a level up. Power cards are not all about "sixes".