-=::) Dante (::=-
My recommended houserule is to play the game as written and simply discard your pre-conceived notions that this is pure market game and not get all strung out over how the market mechanics don't match what you expected them to.
The designers themselves recognized there was a real issue and have addressed it with a rule change in the new expansion.
We've addressed this in Tesla vs. Edison: Powering Up!
by removing "Trade Stock" as an action, and instead allowing each player (in fame order) a chance to trade stock during bookkeeping. In addition, since it's no longer tied to luminary's $ rating, there's no discount/benefit included, so there's less arbitrage.
In testing this has led to a much more balanced game
Pretty sure this doesn't require the expansion to implement either.