Basically prior to philidor most people thought of pawns as just being something in the way. but i think your specific question about the Sicilian needs to take into account that the sicilian was regarded as sub-optimal until the early 1900's. because of this- analysis was very limited, but upon the sicilian itself becoming more popular more analysis was thus warranted and new plans were devised.
Sicilian defense question
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People realized that using pawns to break open lines was a better plan than they had thought.
The biggest revolutions in the Sicilian occured in the 50's with the rise of the Soviet School. Headed by Botvinik, Keres, and Bronstein, among others.
That is when they proved many "inferior" openings were in fact good despite whatever positional drawbacks they may have. Provided they offered sufficient piece play.
In the sicilian defense, I know that the old plan for white was to develop his queen to f3 and play for a kingside attack with his pieces. When did the modern plan of playing moves like f2-f4 and g2-g4 come into existence and how come it was dismissed for so many years?