Worried about channel ghosting in DAQ system - Need unit gain buffer?
If I understand your question correctly, your cautious predecessors have put unity gain buffers to reduce the source impedance seen by the mux.  You have concerns that these buffers aren't needed.  Make an experiment.  Temporarily remove the buffers and replace them with shorts.  Compare measurements with and without buffers (all other things being equal).

p.s.
I wonder why you're worried about these buffers in the first place?
Why are you worried about this test hardware being as cheap as possible?  This is a one-off test boards.
The buffers are already there.  Not that you need to add them.  It ain't broke.