I think the most important tip to remember with flouros is that the light degrades rapidly with each inch it travels from the bulb. To get the most out of the light, you want the bulb to be as close as you can have it to the plant without getting things too hot. That sounds easy, but it involves a lot of daily adjustments.
As for reflective material, I would say that the disadvantages of blocking air flow and trapping heat would outweigh the advantages gained from any extra light.
To get more light, you'd need to add more light. Any fluorescent fixture is better than nothing, like cheap shop lights.
Another idea is to buy a few clip lights:
And then screw a spiral CFL into the clip light. It's easy to attach and adjust.