Below is a link to a great article on the recent boom in Vancouver laneway housing.
Adding a laneway house will increase your property's assessed value thus increasing your property taxes and insurance. However when you consider that you can build a 500 sq ft laneway home for $225,000-$250,000 (remember you already own the land) and rent it for $1,500 to $1,800 a month depending on the area, i've seen larger 700 sq ft homes on the West side rent for over $2,000 month. That’s a nice positive cash flow to help offset the high price of owning a detached property in Vancouver.