But is vastly improved public transportation, an expanded network, revitalised public realm and increased income from the tourism industry "optional" for the future?
That's a false choice fallacy. It's not either/or. There are more straightforward, less expensive ways to get all of those things.
Re: Barcelona, it's often held up as the ONE exception to the rule that hosting the Olympics is a net loss for a city. The fact that there is only one city is a big red flag in itself, plus, it's very debatable whether the Barcelona claims are even true. It's one of those "depends how you count it" situations. The fact that EVERY other Olympics leads to cost overruns is a giant flashing "DANGER" sign.
When cities host the Olympics, they don't just pay for the infrastructure they want or need (that is, if they get any of the infrastructure they want or need). They also pay for:
1) infrastructure that is suited only to Olympic purposes and may be useless afterwards, or best get minimally used
2) the bid itself, which can cost over $100million
3) marketing and promotional costs
4) security (which after the G20 we can safely assume would cost over $1B)
Plus the opportunity cost of all the things that could have been done with that money. Plus the economic costs of the 7-year construction/traffic nightmare period which hurts many small businesses. Plus the ongoing hassle for the people who live there.
If the money is "available" for the Olympics, it's available for other purposes as well. Just like if you have money to go on vacation, then you have money to pay your rent. Want more tourism in Toronto? That $1B security budget would buy a spectacular marketing campaign.
Here's a clip re: the costs London was racking up FIVE YEARS ago. It only got worse from there.
http://www.youtube.com/watch?v=zDbvIj3VyO0
Remember, YOU will pay for this. Do you really want to buy a car just to get a free cell phone?