Sorry I never replied to these messages, but I did read them all and has given me some ideas for future trips. In the end, I had no time to book a last minute holiday.
Travelling as a foot passenger on the Dover-Calais route just seems very inconvenient, even living nearby in east Kent. Not only would I have to walk from Dover town centre (or get a taxi, which i'm never very keen on) as there is no bus service (even though the Eastern Docks is apparently Dover's largest employer), it seems like a lot of waiting at the terminal. Although at least at the other end in Calais, there is a relatively useful bus service stopping near the terminal. The ferry from Newhaven seems a bit more civilised.