The Coopers kits he is talking about are prehopped extract kits, they are the most common form of homebrewing in the UK but do not seem widely used in the US.
These kits give a pretty good quality of beer but it will still not be comercial quality.
I have made a few of the Coopers kits including the Canadian Blonde and the Bavarian Pilsner. I would not recommend trying to add extra sugar above what is called for, but I would strongly recommend using dry malt extract instead of sugar. The best results I achieved with these kits was using the Muntons beer kit enhancer pack, it is 1kg of mixed dry malts designed to be added to any canned kit. This added to the Bavarian Coopers kit made a very nice beer!
What exactly are you trying to achieve with the higher alcohol levels anyway? All I see that doing is making your beer not taste too pleasant.