Interesting ideas. You can try to design the whole chapter pack or cycle of cards if you and your friends are into design (I know that some MtG players do that for fun from time to time).
If you want your ideas to be discussed more you can try to repost this in "General Discussion" or "Deck Building" sections since I'm not sure how many people look at the messages that are at the bottom of "A Game of Thrones" main forum page (usually people go into subforums of interest, specifically most posts are posted and answered in "General Discussion" one).
About cards themselves:
1 and 2 interesting, not sure that they are powerful enough, so probably don't require balancing^___^. 1st one doesn't really matter a lot since even though there are situations when 2 Kings are in play, people wouldn't really consider the whole plot in order to change Duplicate text. 2nd
3. This one rises question of how people are supposed to remember which character it was used on in previous turn (I guess you can change this attachment's text to "you move this attachment to character on the winning side" and then start piling up tokens on that character as sign of his weakness with text like "character gets -1 STR for each gold token on it)
4. "non-King/Queen non-Maester character" is a bit of too much of definition for a card and the design seems to be too centered on restrictions. I know that this way it adds flavor and allows to add more balance, but it also makes it harder to enjoy/play with. I'd say that based on what I learned from Magic, best design cards are cards that grasp the core of mechanic/effect they want to project onto the gameplay while using minimum number of words for that (like, "When you play this event target character gains +2STR till the end of phase" is a better designed card than "When you play this event target non-Maester character gets +6STR till the end of challenge phase if there are no Army characters in play").
5. I think it sounds pretty good. Not sure if at 3 gold just first part wouldn't make this a very strong location (Haven't looked at distribution of Kingsguard charcters for a long time). Or too weak since you need to have a King in play
PS. Hope you don't take my critisism too personally, 'cause I like your idea of designing cards and I think of card designs for AGoT and MtG all the time (though most of them suck, IMHO=). So if you manage to design a card set, balance it and add to the game for casual players (even if it won't be legal for the tournaments), I'd be very interested to look at the final result (and so would be a looot of players).
PPS. Look up Adam ''Bone" on this forum or agotcards.org forums (there are a few threads there about card design) since he seems to have a lot of interest in discussing card designs and new ideas.