As this article in StrategyPage points out, Iran is already doing plenty to prop up the Assad regime in Syria. But Assad's wish list contains some truly frightening things and Iran isn't crazy enough to accommodate him:
Iran has disappointed its long-time ally Syria. Despite sending cash, security/intelligence specialists, weapons and other supplies, Syria feels that Iran could do more. Actually, Syria is pleading with Iran to do more, otherwise the Shia minority that has ruled Syria for decades will be no more, and Iran will lose a key ally in its effort to become the leader of the Islamic war. Syria wants Iran to create a state of war against the Gulf Arab states and coerce them to stop supplying Syrian rebels with money and weapons. Iran can't do this without risking a real war and that would make it clear what a massive fraud Iranian military power is. Western intelligence agencies know, from satellite, electronic eavesdropping and a large number of human informants what shape the Iranian armed forces are really in. While many of the Iranian troops are first rate, their equipment is largely obsolete or shoddy locally made stuff and their commanders are appointed more for their loyalty than for their military skills.
Syria also hoped Iran would order its Lebanese client Hezbollah to attack Israel again, as it had in 2006. But Hezbollah does not want another war with Israel, at least not yet. The Israelis have been preparing for another war, and will not be surprised by Hezbollah preparations as they were in 2006. Hezbollah points out that if there were another war, Hezbollah could no longer provide armed men and access to supplies via southern Lebanon (which Hezbollah controls.) Still, the Assad dictatorship in Syria expected more and, in fact, needs more help to survive. While the fall of the Assad government will hurt Hezbollah, the damage will not be as great as would be inflicted by another war with Israel right now.
Creating a state of war against Saudi Arabia would be an extremely dangerous course of action, as it would necessarily involve the west whose oil supplies would be at risk. And Hassan Nasrallah, Hezb'allah spiritual leader, isn't dumb enough to attack Israel -- even at the behest of his paymasters in Tehran. Iran is already finding it difficult to resupply their ally in Syria and a war in southern Lebanon would cut off most of those supplies.
It's obvious Assad is desperate and is casting about for distractions from his plight. If Iran doesn't want to go down with him, they won't get anymore involved than they already are.