Western powers want a regime change, they want the old pro-western regime back before Khomeini came to power, and it is very important.
As Syria will get rid of ISIS and other extremist groups they will begin rebuilding, and there are may regions that have different influence, from Russia,NATO,Iran, and those countries will help financially with rebuilding, but if Iran is in turmoil or goes pro-western, the sphere of influence will be bigger in the region.