This might be a good one for the “feature request” area. I tried a few options like turning off the recording to work out the current values, but you have to go back a frame as well. (So you could turn off recording, go back a frame, work out new positions in your head, go forward a frame, go back into record mode, position things, record that, ... ugly!)
I think you really want a fourth mode (stop, play, record, and stop-frame-recording). For stop-frame recording I agree you want to see exactly what the previous frame was so you can adjust it. When scrubbing through the timeline in this new mode I guess it should also show the previous frame all the time. This is a mode purely for stop frame recording. (You could get fancy and show the current and previous N frames as transparencies or something...)
(I was wondering if something like this possibly useful for general scrubbing if you want to adjust (overwrite) a draggable. But because there is no key-framing, its probably easier just to re-record that section. It can however be tricky to get the position exactly right if you want to override part of a longer scene, but blending might help there (start the recording a little early and blend into the new real start value). Personally I would like to be able to see and adjust recorded values in a drag - but it really is a request for keyframing draggables rather than what is currently there. E.g. do a single frame record of a draggable (and scale and Position X,Y transforms) every so often, and have CH blend between those single frames. You can do it with blends today, but its rather awkward. But the point is there is a similar problem - you want to know the current values and easily record over them - but going into record mode resets things to defaults for the armed values, making adjustments harder.)
Hmmm. Another idea. (Maybe stupid.) Have a record mode where you see the current frame values. Then new stop-frame record command to move cursor forward before recording the new value. That would then be useful with scrubbing and stop frame recording.
In the March 2018 Tips and Tricks video just released, it shows how you can have two draggers - you arm one for recording, but disarm the other one. In this case you see the value of the unarmed dragger. I wonder if you could have two draggers (you add a new dragger behavior) then alternate arming the two draggers frame by frame. Might be worth experimenting with...
Interesting! I will have to take a look and try that out. I really appreciate all the ideas. Thanks!!