The individual reflectors boost light output by about 300% compared to the bulb alone. I don't know how much of an increase it makes over a single reflector but it is significant. Individual reflectors are what give T5 the power to compare to halides, so yes it's well worth the few extra bucks to get them.
It may be more expensive up front, but it'll be a lot cheaper to run. Most halide bulbs are about $60 each, and need to be replaced every 8-10 months or so. The average T5 ho lamp costs about $20 and needs to be replaced every 18-24 months. You also aren't dealing with the heat issues.
-Justin