Elven Princes- What power do they have

[daeron]

Hi guys! I'm new to this. I've searched many threads and not found a satisfactory answer.
Gandalf when supporting Pippin's inclusion into the fellowship says an elven prince like glorfindel could not, with his power break open the gates of Mordor. Well, what power did the elves of the third age have. We have seen elvish power in Lutian and Finrod's songs. But in others we have but seen the skill in warfare and foresight (maybe with few exceptions). Well we actually do not see much 'magic' in ME (The greatest plus point of Tolkien's works). If the greater elves like Elrond, Cirdan and Galadriel do actually have great power, that which does not originate from the rings, how come they never used it in the third age. Also any clues as to the roles of Elves in the last battle of the second age are welcome (apart from normal war).
Is Glorfindel the same as the one who died in gondolin and if so when did he return. If so, he being involved in the kinslaying of Aqualonde should not have been allowed to return, until Dagor Dagorlad. Or atleast that is the fate of the kinslayers as I remember reading.