Having a discussion elsewhere about effect of having a smudge on the front of your lens and thought I would do a rough and ready experiment.
I suspected something like a fingerprint, being translucent, would have a greater effect than something opaque on your front element.
Rather than foul up my front element I chose to use filters. I half covered the filter with the different materials and used the lens wide open, figuring this would maximise the comparison.
I had two types of cellotape to mimic a fingerprint, one a little milkier than the other but not as bad as "invisible tape" As you can see in the master shot both are all but invisible.
So yes I think a fingerprint punches above its weight in mucking up your image.