Predict auditory masking with a crude estimation?
By looking at the spectrum's probability law you are completly missing the temporal information in the two signal you wish to compare thus it would be a bad predictor.
Imagine you analyse two 2048 pts signal, one is null during the last 1024 points whereas the other one is null during the first 1024 pts, they could have the exact same spectrum but they won't interfere each other at all.
This is the whole purpose of time-frequency analysis, unless you have some a priori knowledge, you can't avoid using a short time fft.