Lies, all lies. I have had S model bumpers on a base. Some people have swapped S front brake calipers onto a base. I have red (base) brakes on one of my '99s and In plan to paint the brakes on my S yellow. It's not hard to replace a gauge face or the whole cluster and trim pieces. There are some base models that have the six speed transmission swapped into them. Oil coolers from 3.2s have been swapped onto 2.5s and 2.7s.
Truth: Correct that an S model VIN will start with WP0CB... and a Base will start with WP0CA... .
S has heavier driveshafts and some suspension parts. Woody posted a great thread outlining some of the underlying hardware differences:
http://986forum.com/forums/performance-technical-chat/53067-pictorial-differences-between-base-s-model-boxster.html
I bought an actual S model without realizing that it had a 1997 2.5L engine in it and I had already owned and worked on Boxsters.
Want to be sure of what you are getting? Have a reputable shop do a pre-purchase inspection (PPI).