I have a difficult time envisioning 2/3 of Aes Sedai as "normal people who go about their lives." Even Aes Sedai that are (for the most part) permanently in the Tower attempt to manipulate nations and politics from afar, and consider themselves the puppet-masters of the world (the possible exception to this being those of the Brown Ajah - we've seen members of every other Ajah meddle in world politics). Organizationally, they are a mess, and this is not only because of leadership issues - although that is a significant problem. Elaida's actions, idiotic as they may be, are probably similar to what a large number of Aes Sedai would do in her place, if given the opportunity. This point seems to be supported by the fact that, although her blunders appear enormously damaging to the Tower from a reader's perspective, she has not been overthrown by her supporters. This seems to indicate that, although the results have been far from ideal, the decision-making behind her actions is largely in accordance with the opinions and perspectives of her followers. And although she is gradually losing the support of her followers in the Tower, I would argue that this is because of disastrous results and not necessarily poor decision-making. Siuan, on the other hand, was overthrown merely for conspiring to let the Dragon Reborn run loose in the world - something considered anathema to just about all Aes Sedai. Elaida's attempts to deal with Rand and the Black Tower, colossal defeats though they were, falls into line with the sentiments expressed by most Aes Sedai over the course of the series: the Dragon Reborn should be under the control of the White Tower, and men who channel should be dealt with - whatever the cost. Their refusal as an organization to admit that they have lost control over events has created innumerable problems in the series for the side of the Light.

I would say the series is a "giant soup" of deeds, and I will not go farther than that. Although the fundamental basis of the series is good versus evil, there is too much that falls in the gray area between these two polar opposites to definitively categorize most actions as either "good" or "evil." You're right in saying that it is one dimensional to say the Aes Sedai have had a minimal positive impact on the series, because to do so is a denial of perspective. Even the most delusional of Aes Sedai believe what they are doing is in the best interests of others. It is difficult to characterize Elaida's misguided attempts at restoring Aes Sedai control as "evil," but from the viewpoint of the main characters, the actions of most Aes Sedai absolutely impact them negatively. As an organization, Aes Sedai are supposed to be responsible for protecting the world from the Shadow; this charge is a part of a number of their rituals and ceremonies - one of the titles of the Amyrlin is the "Watcher of the Seals." Despite this, the White Tower as an organization has done nearly nothing to fight the Shadow in the series, even though all signs point to Tarmon Gai'don being in the very near future. Instead of working together to deal with problems with the world on the line, the White Tower has deteriorated into Ajah politics and even civil war. You are right in attributing some of this dysfunction to workings of the Black Ajah, but more than enough of it is the product of Aes Sedai arrogance and refusal to cooperate. Look at the Salidar delegation sent to Rand. They stand in stark contrast to the delegation sent by Elaida, but they nevertheless failed to entice Rand into an alliance they desperately needed (and acknowledged they desperately needed) because they refused to submit to Rand's very simple demands, and squandered their chances at forging an alliance in a meaningless power struggle to prove they could not be intimidated. This group ended up being useful to Rand in the series only because he forced them to obey him with oaths of fealty, the result of blatantly defying his restrictions on the number of Aes Sedai to follow him to Cairhien. As it stands right now, Rand does not have a formal alliance with Egwene because of this stubborn refusal to relinquish their claims to authority.

Of course, there are some notable exceptions to this, as mentioned previously, but these are all examples of Aes Sedai acting independently of the will of the Hall and Tower. Even Moiraine, who did more than perhaps any other Aes Sedai toward helping the main characters do what they must do, and therefore helping the world survive, tried to manipulate the characters initially, and admitted in her final letter to Rand that her attempts to control him were wrong. For the most part, Aes Sedai have made greater nuisances of themselves than members any other group, from the perspective of the main characters. All of this cannot be attributed to the Black Ajah - we have seen that other groups have been thoroughly infiltrated by Darkfriends, and yet no other organization has created so many problems. The Seanchan are not a group dedicated to fighting the Shadow, so their actions are understandable. The Whitecloaks, however, are a good example, and are very similar to the Aes Sedai in more ways than they would like. The organizational incompetence of both groups is unbelievable, but Aes Sedai are never supposed to be incompetent, while Whitecloaks are only soldiers with a perverted sense of justice. And while Jaichim Carridin may occasionally cause some problems, sadly it is the Whitecloaks themselves that are counterproductive to their own efforts and any intention they may have to fight the Shadow. The same is true of Aes Sedai, and while other groups have certainly created problems for the main characters (in particular the nobles of just about every land conquered by Rand), Aes Sedai hold themselves to a higher standard than everyone else, and should be judged according to that standard.