I'm going to go with the minority here and say that yes YABU.
Despite costing £9.3bn the vast majority of that does not go into the games itself, but will be used to build and regenerate a severely disadvantaged area of the country.
Within a year of the olympics being over the area will be benefiting from new housing and flats, a new swimming pool and fitness centre for the area, new outdoor athletics and team sports facilities for use by the local people and schools, a stadium which is likely to be sold either to a football team or concert organisers and a couple of stadiums which will be moved and re-built in other areas of the country to provide sporting facilities to other disadvantaged communities.
Beyond that, the whole of the surrounding area is benefiting from improved transport links, a conservation area developed by removing a lot of pollution and litter and maintaining the canal system. The games will also be very friendly to the environment.
This is all in one of the most deprived areas in the country, where unemployment and poverty has been a serious issue compounded by the sheer density of the population.
There are a host of other things I would like to see removed/ cut/ stopped before the olympics. For example - councils spending money on surveillance to catch people who over stuff their bins, who don't recycle properly, or who apply to schools out of their catchment area, or maybe the enormous sums spent on needlessly collecting vast amounts of 'data and reporting' adding buerocracy to an already cramped system.
I kind of agree with you on the benefits point though. I would never want to see money taken away from people who don't need it. The problem is that there are numerous examples of people cheating the system, taking what they aren't entitled to, or getting so much money/ assistance that they earn more than the average wage - this is what needs tackling.
Oh and before you say it - no I don't work for the olympics!!!