Granted there is a lot you can learn from beginners and for sure you can get just as good a workout with someone who has a years less Aikido as you can with someone who has a year more but - feel good sentiments aside - I would rather spend a lot less time with beginners than I do now.
1.) beginner or not - I always reserve a chunk of my practice time for basics. You can not get the most out of this if your partner needs to be tutored. What you do need to do is establish a rythme in order to perfect the basics. For that to happen your partner needs more than half a clue and a reasonable amount of confidence.
2.) Beginners do have predicatable ukemi. However, because you have to be slow and even more careful than normal there reactions are as stilted as your technique has to become. If I want to slow my technique down I specifically do that with as an advanced partner as I can find.
I like my beginning students - I invest a lot of time not because they are beginning students but because a good number of them will be good training partners. The rest are the price I have to pay. I have no problems with my seniors viewing me the same way.