When are you coming? The reason I ask is because the Tea Plantation has very limited times that it's open to the public and the summer is not prime time for them.
The carriage tours start at $20 per person, but they are interesting. Two things you need to know about them...if it's seriously hot, they can't work the horses and will shut down for the day. And there are 4 zones that the carriages work and they go on a lottery. Some tours are better than others, but you can't pick which one you take. If there is a particular house you are interested in, you can tour it by foot.
The ghost tours are interesting, if you enjoy that kind of thing. The Old Exchange Post is kind of neat for the same reasons.
We have lots and lots of shopping between King and Market streets, and if you're here on a Saturday morning, the farmer's market in Marion Square is lots of fun.