My perceptions of WAAS, turned off selective availability, etc. is
that you in many cases are still using and co-relating to charts that
were constructed using hand thrown lead lines and surveying instruments
(sometimes on a pitching deck). Especially when using vector charts the
magnification possible with such charts completely overwhelms the
'resolution' accuracy .... and can very quickly put yourself firmly
onto a reef, rock, or channel berm. Jeeze, most of the coastal charts
used in the USA are based on the NAD27/29 data (many of which were
simply transcibed from pre-colonial charts .... and were NOT verified
by 'modern' means).

Running an unfamiliar channel, close approach to a hazzard, etc. by the
sole means of GPS (even with WAAS etc.) is GOING to 'catch you'.