On some of the times I have been there, I have seen these carriages and I personally think they are great from a horse-lover point of view. They give the park a classic feel which is what Walt Disney intended when he built the first of the Disney parks in California.
Very enjoyable if you want to take the weight off your feet for a while. They could be well needed.
Always worth a trip along Main Street. They are not always out but nice to ride and see when they are. Not always easy to get on but try going the ‘wrong’ way (i.e. in the morning get on at Central Plazza and go back to the Station, everyone else is trying to go the other way!) and then your more likely to get on.
Great add to Main Street USA. It gives that classical feeling to it. They are not always running, so you should inform within the City Hall if they are running for your stay. Enjoyable for big and small.