My opinion:
Fighting in the D: Fights happen in bars, so if some folks get into a drunken fist fight it wouldn't be abnormal. However, there are clearly things in place to prevent powers so that's an entirely different scenario. I simply don't get myself into such a situation.
RP by Level: Case by case. Even though I have a 50, whom I don't RP on, I don't consider that to be godly. If a level 25 was well trained with a sniper rifle for example, I'd be concerned regardless of my level. I'm fine with somebody saying they're more difficult to deal with because of having a great deal of experience, but if somebody is extremely arrogant with the "I'm 50 +1 thus you can't touch me" I ignore them. You're not that special.
Powers not in game: Case by case. If it's RPed well, isn't OP and it makes sense, why not? If it's absurd then politely inform them of such. Sometimes adding those things in can enhance RP, again, if done correctly.
Psi/Stealth: Probably should have mutual consent when it comes to this. Personally my main doesn't have superior vision or anything protecting his mind. Though, if you start doing things to my character without permission then I'll simply ignore you. I think it's poor taste to say you're completely immune to it or can see anything regardless of external factors.
One last note: I tend to ignore those that RP son/daughter of famous Gods or other figures; in the RP world that's typically a big no-no. Saying you're the grandson of Zeus is no different than claiming to be Statesman's son... you just don't do it. There's an awful lot of those in the D, one in particular apparently has the power of many Gods, is immune to Earth powers and can resist physical damage... at least something along those lines, I can't read the profile for reference. There's no way I can take that player seriously.
At any rate, I was a bit rushed so I don't expect that all to make sense. Happy RPing!
