One minor clarification: there are three aspects of the "smart" search expansion -- keyword to keyword substitution, keyword to item specifics matching, and keyword to category substitution. The problem seems to be with keyword to keyword substitution leading to unwanted extra matches appearing in the search results.
Adding an exclusion term bypasses all the "smart search" features and eliminates the inappropriate keyword substitution (but also potentially appropriate keywords as well, unfortunately).
One possible consequence -- if you are using the keyword to category substitution to limit your results to a particular category, adding an exclusion term will undo that and you will see results from all categories in the new search, which may not be what you want.
If adding an exclusion term limits your search too much (by eliminating wanted alternate spellings, for instance), try instead using your original search terms but in backwards order. That seems to work in cases where some search terms are grouped as compound terms. So instead of searching for "Pee Wee Herman" (without quotes) which produces over a million unrelated results, try searching for "Herman Pee Wee" which returns 2500 appropriate results. By avoiding the exclusion term, you can still get the benefit of keyword substitution to find alternate spellings.
