Elena was also brought back to life through that magic sacrifice Bonnie did that linked John Gilbert's (her biological father) life force to Elena so when he died she came back to life but I don't think she never saw any ghosts because of that nor will Katherine.
I'm not sure about the rules exactly but the magic has to be tainted for the consquences to happen. The gilbert rings revive you some time after you've died and I don't think Alaric ever saw any ghosts (except for Esther when she was preparing him) either and Jeremy didn't see any up until Bonnie revived him specifically with her hands and just after he died.
Yeah but it keeps it interesting. :-)
I think something is consistent and that's when you use a direct revive spell the victim in question will suffer some consequences like become a medium because direct spells require too much energy. A witch that utilize different power sources than themselves (expression) or their own magic (spirit magic?) can conjure more powerful magic like using other elements like celestial events, fire, water, other witches (channeling), sun, trees and possibly other things we don't know about.
Considering love and death are strong themes in this show I suspect those can be used as well.
A Medium is a person who can see ghosts. Known Mediums are Jeremy and presumably Matt, since he was able to see the ghost of Vicki. A person becomes a medium by dying and getting resurrected. Bonnie resurrected Jeremy when Sherrif Forbes accidentally shot him, and Matt almost died and Bonnie brought him back, thus enabling him to become a Medium.
Since Katherine didn't die and get resurrected (I'm not counting the cure), she normally can't or won't be able to see ghosts. You never know, maybe Julie Plec is reading ths and thinking of making Katherine a Medium.
I am hoping for this so she can see Kol and there are more interaction with ghosts other than Jeremy.
What do you think?