Treating one would probably better than treating none. Blocking the synergistic effect would be a great step forward, but I don't think we'll see that for a long time. Immuno-depressed cancer patients are succeptible to all kinds of common viruses and we cannot currently do much to help.
I wonder if we should seek out getting colds, to improve our resistance to SARS.
You guys should know I'm just speculating here. Some viruses have trouble re-infecting a person once that person had the virus (ie: chicken pox). However, there are people who get re-infected even if they have had it before (ie: Shingles). Staying healthy by exercise and proper diet are the best bet. Seeking out a cold is not productive at all.
IMO, SARS is here. I would bet that it's much more widespread than we think and that some people are not even showing 'classic' symptoms. The cases that are being reported are the cases where an opportunistic, secondary virus is causing hospitalization and even death.