"...method for jumping from keyframe to keyframe within the Key Graph Editor"
CTRL Right or Left arrow.
"...method for copying keyframes from an attribute, at one point in a playback range, and then pasting the copied keyframes to the same attribute but at a different time"
You can copy all keyframes from any attribute that has keyframes (bolded) and paste to other objects or the same object. Pasting to the same object it would only be apparent if after you have copied the keyframes you move the keyframes (CTRL drag - values or Shift CTRL drag - time). So it's not exactly what you want but workable. Also you can copy and paste individual values of keyframes which would work just be more steps.
#XPression