Market Collector interest in South Carolina and Georgia jockey for last place. All things being equal, South Carolina is probably worse. The are few collectors, and what few collectors there are seem to focus only on very narrow areas. There is some interest in Charleston. This is a very wide open field.
Research is less advanced for South Carolina than any other state.
A good post office listing will help. Material has never been common, and there may now be problems supplying the new demand. Nineteenth Century covers are in especially strong demand.