That's the idea,don't forget also each "unused" oyster card also cost £5 as well as any unused balance. Plenty of tourists both domestic and from abroad buy the cards to save money on their fares while in London then leave the capital leaving the cards(worth £5) & unused balance in TFLs coffers.
That could be quite true. I have got an Oyster card with auto top-up and the last time I topped it up was at the end of 2009 with £20, normally I use my Freedom pass but because the Central line was messed up the other day I had to use National Rail from Paddington to Hanwell because the Freedom pass won't be accepted before 09:30 and I've still got £7.59 left on the Oyster.
That would be the main holder of these residual items- plus I guess a fair number of deceased holders. What happens in this case I am not sure- can the executor claim back any unused funds? Would they bother?
Could some of this money be put to good use improving LT? Each weekend, especially Bank Holidays, it is sooooo time consuming, trying to get round London on route that have no works. I have found a route that "they" don't seem to have noticed so it is still there! Seriously there is a lot that could be done with £30m, that would improve life for the consumer.