I'm a frequent flyer, but on the BA scheme rather than Cathay (I haven't switched as the BA scheme records all tier points earned over lifetime and once a certain (very large) level is reached, they award Lifetime BA Gold - which is equivalent to Marco Polo Platinum).
I agree the best value is through upgrades rather than travelling economy. The J and W air miles flights do book up quickly though, especially for holiday periods. My tip would be that even if there is no availability for your preferred route on your initial search, you should keep checking back from time to time, as more redemption seats are often released nearer the date of travel depending on how booked up the flights are. Last year, about this time of year, I managed to get two return business class redemption flights HKG to LHR on Cathay for Christmas (though we had to route via AMS on the return leg) on my third search.
I don't know if Cathay has a similar scheme, but I also use my air miles on short haul BA under their Reward Flight Saver scheme, which gets me to most short haul destinations for just 8,000 miles plus GBP 35 per booking to cover all taxes and surcharges, which I think is also pretty good value, as the taxes are often more than this alone.