Tom Watson MP points to a story about Australian PM, John Howard, getting embroiled in a row bout spam. My reading of this story is that it doesn't sound much like spam.
You have to be very careful what you define as "spam". Direct mail is a legitimate marketing/campaigning tool if, AND ONLY IF, it is targeted. Simplistic research such as asking people if they want to receive spam or direct mail nearly always results in "no". However, more sophisticated research and focus groups usually results in the opposite answer.
For example people do want to hear about special offers on a product they normally buy. They do want to hear from local politicians about an issue that effects their street or town. Unsolicited mail can be welcome if it is relevant.
The other issue is that under the Australian legislation it is OK for political parties to send unsolicited email, Howard's problem was that he used a professional company to do it. I just don't see the problem in getting the job done properly.
It is right for political parties to be able to communicate with electors. One of the most common complaints by voters is that they only ever hear or see from politicians at election time. Email and the web are both excellent solutions to this. It is by far and away the easiest and cheapest way to keep in touch. In an ideal world you would knock on doors, phone and deliver leaflets more often. But it is simply too expensive in both time and money. The only real draw back to email and the web is that still not enough people are 'connected', but this is improving over time.