JillA - you can click "Notify" next to "Reply" on the topic tabs. That will send an email to the address you provided to the site on signup saying that a new reply has been made to the topic. I use it to stay on topic of replies to threads I am following, and especially for this one, since I update the charts.
The simple answer is that no, you don't need a certain income to sponsor your spouse. In CIC terms, you do not need to meet a specific Low Income Cut Off (LICO) point in order to qualify as a spousal sponsor. However, you cannot be in receipt of social assistance for reasons other than disability, nor can you be an undischarged bankrupt. Furthermore, if your income is on the low end, and your spouse cannot show that they have income-earning skills (such as a job history, or a good command of the English language) you may run into a Section A39 situation.
Section A39 gives CIC the power to deny a spousal sponsorship if they feel that the spouse is unwilling or unable to support themselves and the Canadian sponsor has not provided adequate proof that arrangements not involving reliance on social assistance have been made to care for their needs. There was one such case on CanLII where the wife had no English language skills, had never worked outside the home, and her spouse himself had never held more than low-income jobs, did not have a home of his own or any significant savings. The sponsorship was denied and the denial was upheld on appeal, because in between the denial and the appeal hearing, nothing had changed in their situation.
Anyways, sorry if that was overly detailed, just wanted you to have a full picture of how the income thing works for spousal sponsorships.