Without the neon sign, you'll need around 200 billion shares to max out everything. For the level-101-sign it's almost 10 quadrillion shares!
(if I calculated everything right and - like you said - if the wikia is correct)
So... it's as insane as it is useless to max out the sign. Its share-multiplier only helps when you're always selling your company after a short period of time. But since you're bound to use the stock market to reach the higher decoration-levels and to give up the futile sell-sell-sell-strategy most players seem to use... well, you probably see why there's no real benefit in this. When everything is at level 101, you just don't need the shares anymore. As long as they aren't adding more decorations.
And buying/selling stocks for ~1 month longer (assuming you're going up ~1200 levels per day), when you're already at 200B shares... okay, *I* am going to do this. But it is meaningless nevertheless. If you can live with the nagging feeling of imperfection and a prestige bonus slighty below the maximum.