Hello panda and welcome to the board. I do like those pieces, they look so simple and functional yet still have a grace about them. I've not been able to find out much about Okigwi Pottery other than it was set up by a well-known British potter called Michael Cardew in 1950-52, who had been sent out Nigeria to help develop potteries there. The story can be read online here:
http://www.ceramicstoday.com/articles/cardew.htm. Pottery has long been made in Nigeria, mainly by the women using their traditional methods, but Cardew and his colleagues introduced new methods of potting and helped expand the range of pottery made there.
I can't help with collectability (or value) as I simply don't know, but my guess is, that like all things, it will have its devotees who will be prepared to buy for their collections. A search of the usual sales venues such as eBay may give you some insight into how sought-after it is and what sort of prices it brings.
Hope this helps.
