Hi Rickster,
You most certainly are not the only person who wouldn't be doing the add-on for the trip - there are 8 people booked for Inspirational China alone.
Yes you will need a Chinese Visa, whether you do the add-on or not.
There are currently no compulsory vaccinations for travel to China however we strongly recommend that you consult with your General Practitioner or Practice Nurse who will assess your particular health risks before recommending vaccines. This is also a good opportunity to discuss important travel health issues including safe food and water, accidents and insect bites. Many of the problems experienced by travellers cannot be prevented by vaccinations and other preventive measures need to be taken.
Kindest reagrds,
Monty