Can higher doses of Effexor (venlafaxine) (above 75mg) cause depression to worsen and/or increase symptoms like anhedonia, lethargy, demotivation, etc.?

Not typically. Increasing Effexor (venlafaxine) dose may not be effective and can increase side effects, including anxiety, but should not actually worsen depressive symptoms you describe. Effexor (venlafaxine) can unmask Mania in a patient with underlying Bipolar disorder.