Individual letters count more than collective respresentation. Lobbying your local councillor is also a good move especially if he/she is on the planning committee.
Individual letters count for nothing from my experience

Don't bother contacting your local councillors either...I tried that and am still waiting for a reply 4 weeks later, I really don't expect a response at all...I've never come across such a useless bunch

My problem is nothing to do with the Quadrant, which I think stands a very good chance of going through on the first attempt.
If it doesn't then Pickles will be sure to pass it on appeal, IMO :dan