This all sounds very unfortunate.
If a sempai is flooding you with information, say something like 'there seem to be too many points to keep in my head at one time'. He will either get the message or he will start philosophising for the next hour about your mind being one with your body. If you socially interact (i.e. outside the dojo) you could tell him/her straight that you find it difficult to follow all these ideas at once; which should improve everyones training. I'm always pushing people to give me feedback on their training, so if your sensei is trying to get you to learn rather than trying to demonstrate his/her own skill, they should welcome any particular comments (though best to avoid any direct criticism in the dojo).
As far as rough higher grades go - this can be very disconcerting. Again, saying something like 'I'm finding that comes on too fast' may work. Aiki is a sharing experience where you are both supposed to learn. Sometimes higher grades can be selfishly proving to themselves that a technique works despite the fact that it is causing increased tension in uke (and often developing a submissive reaction which would not realistically occur), and may result in them not training with you in future; which is a loss to both of you.
I suppose the take home message is; no matter what level we're at, we still have as much to learn from each other.