Parshas Shekalim and Purim
I wish to look at a different point. "Reish Lakish said, 'It is revealed and known to He who created the world that Haman was destined to measure shkalim on Yisrael; therfore, He brought their shkalim before his, as we learn that on the first of Adar we read Shkaim'" [Megillah 13b]. So the shkalim given by Yisrael counterbalanced those of their adversary. Haman could have made the case that he was offering the same sum as Yisrael, so his money should count just as much as theirs.
But one of the key lessons is that the whole -- the entity of klal Yisrael -- so much exceeds the sum of its parts. The 1/2 shekel illustrates the point that the parts have to combine to make a whole. It's not just a matter of "no man is an island" but an interconnectedness that brings together the separate strands to form something that is more than just a gathering of pieces -- like the reeds woven together to form a basket. And each Jew has an equally important part in making up the whole, which is why all must give the same 1/2 shekel -- neither more nor less -- whether you are wealthy enough to endow the building or poor enough to have to fit this amount into your budget for the month.
That is what makes this particular contribution so pure. It is given with no hope of personal distinction. It does not augment one's status to say, "I gave 1/2 shekel," for the rejoinder would perforce be, "Well, so did everyone else!" One does not get any recognition like a plaque or journal ad for this yearly contribution, in which everyone counts equally. There is no contest to prove one's worth by giving an impressive amount. That is not an option for the 1/2 shekel offering. It is a reflection of each individual's worth becoming great as an indispensable component of klal Yisrael.
That is something Haman was completely unaware of. He sought self-aggrandizement by showing how he alone could match the amount of money offered by all the Jews together. But he completely missed the greatness of the forest by only seeing separate trees. It is not the money but the cohesiveness of the people it represents that makes the 1/2 shekel so valuable in Hashem's eyes.