You have a Skyline document with a spectral library. The "PrecursorResults.TotalArea" thing would have been the right answer if you had used Skyline to extract chromatograms from raw files.
It sounds like you want the MS1 intensities of the peaks that were selected for fragmentation in the results that were used to build the spectral library.
MS1 intensities do not get stored in the .blib file, so there is no way for Skyline to give you that information. Currently, Skyline does not make it easy to get any information out of the spectral library. In the future, I could imagine that we might have something similar to the Document Grid, but for spectral libraries, that would let you output lots of information from spectral libraries.
Currently, the only way to get information out of a .blib file would be to use database tools on it. The .blib file is a SQLite database. The fragment intensities are stored in a compressed binary blob which you would have to write code to interpret. But, nowhere in the .blib is the precursor intensity stored.
It sounds like your best bet is to go back to the OpenSwath results which you built the spectral library from.
I hope this answers your question.