No matter whether the $300 billion comes from the US or the Gulf countries, it would be a grave mistake. A rebuilt and reinvigorated Iranian regime would be far more dangerous than the one we face today.
The greatest lesson of 40+ years of US–China relations is this: the US should never have extended economic support to the Chinese Communist Party before a Regime Change. The same lesson now applies to US–Iran relations.
Totalitarian regimes such as China, North Korea, Cuba, and Iran are like vampires. Invite them through the door, and they will feed on the free world's lifeblood — its innovation — until the well runs dry. With every feeding, their toxins spread, and the free-market economy itself gradually begins to rot from within.