One more way to do the same thing is declaring default element namespase "http://schemas.microsoft.com/sqlserver/2004/07/showplan" in the XQuery:

SELECT t.c.value('@Column', 'varchar(128)') AS 'Parameter', t.c.value('@ParameterCompiledValue', 'varchar(128)') AS 'Value'

from @x.nodes

('

declare default element namespace...