Any bonus needs a negative to make it worthwhile for roleplay.
In the "Freedom Force" games, you could get all sorts of extra skills, but you had to balance them out with weaknesses. Get high resistance to fire, then you'd have to take a high weakness to ice.
Take a movement speed increase and you might have to take "Brittle Bones" which makes you more vulnerable to smashing damage.
In this mindset, take your examples...
4) Wanderer- The more you are by yourself, the more you learn. When you complete a mission solo, you receive an experience bonus.
(NEGATIVE) If you are teamed up on a mission, you get less experience.
3) Vicious Strike When you are alone, sometimes you have to play dirty, just to survive. When you are on a mission solo, you have a slightly increased chance of stunning enemies.
(NEGATIVE) But when you are teamed, your chance of stunning others decreases dramatically and your chance of getting stunned increases.
Superman has Kryptonite, Green Lantern cannot influence things with a yellow color, Spider-Man runs out of web fluid, The Thing is really vulnerable to itching powder, the Hulk is weak against Psionic attacks, Professor Xavier is vulnerable against sonic attacks, Wolverine is plagued by appearing in 20 non-related comicbook continuities in one month, and so on...
Extra bonuses must mean extra weaknesses.
