I'd like to comment on a few things.
First, no one really knows what the vacancy rate is for condos. No one. The best one can do is throw a very very wild guess into the ether and hope it's accurate. Tons of the condos currently being rented have never ever been placed on the MLS (like mine) and never will because paying an agent to rent your place out is one of the silliest things to do and money down the drain unless you own tons of them. So while .8% might reflect condos rented through an agent, I'd guess there's an even larger market out there. 3-4x larger.
Second, while rents are definitely higher for condos for all the reasons you mention, they have been static for the past 8 years (meaning they have dropped in real terms) and are now dropping. I have several friends who have just recently rented brand new condos and they all managed to get either a)free parking, b) a free months rent or c) both. Also, they all rented independent of an agent on either side and the owners were very very willing to negotiate.
Third, I believe I saw Urbanation say that over the next 2 years we will see 37000 units completed in Toronto. While we could say, conservatively, that 14000 will be investment properties (I would peg the number at closer to 18000), what about all the people currently renting condos who will be occupying these newly completed condos. While I won't hazard a guess at the number, I don't think it's insignificant. The possibility even exists that many people will be like myself, in that I and my partner will be vacating 2 condos, to move into the one purchased. This could add 1000's more into the mix.
The one thing that I think is going in favour of currently owned rental condos is the ridiculous price of new construction. When I first bought in 2003, rent was equivalent to a mortgage at around $1500/month - assuming 15% down on a $200 000 condo ($170 000 mortgage). Now, that same equation makes a $1400/month condo cheap compared to the $2400 carrying costs of a $350 000($295000 mortgage)/condo with 15% down.
In order for prices/rents to get back into line with wages, we need a 20+% correction or the equivalent in terms of price stagflation for the next 5+years. Or, I could be completely wrong, and Toronto is now becoming like New York, London, Paris, etc., and real estate downtown is simply out of reach for 95% of the GTA populace.