This closes 14th November. I went up at weekend and was wowed, free to get in to the exhibition, and some days have pay-for lectures on the subject. Well worth a couple of hours of your time if you're in the city, the exhibition includes some of his World War 1 artworks which are very seldom shown.
Spare also features on the BBC Culture Show in the coming week (probably also watchable afterwards on i-player) and a documentary film is in production, and Phil Baker's biography comes out this month. Good Times for Sparophiles : )
http://www.southwark.gov.uk/info/200162/the_cuming_museum/1607/temporary_exhibitions/2