Thanks CP!
Thanks for the links! It seems the biggest factors in having this done is whether the house is old (not sure what numbers to base this on) and the size (accessible vents).
My place is only 11 years old and relatively small in size ~1700sq.ft. I can vacuum most of the system myself, and keep the furnace filters changed every 30-60 days depending on furnace/a.c. use.
The cmhc article raises a good point. The dust in your house is a direct result of the occupants of the house bringing it in from the outdoors. Therefore the best way to reduce dust/pollens/danders etc. is to keep it to a minimum from the get go. Keep carpets clean/vacuumed, avoid open windows when possible for extended periods, keep shoes, coats etc. in a closet at the front door. These are all things we already do, and the wife is great at keeping up the housework!
For my situation it seems to be more peace of mind rather than an effective service. Don't think I'll do it.
Cheers