Yes, nothing meant nothing, not a surface with white paint, nor white plastic. However, since a 50% gain over nothing (nothing is still nothing) is possible I'll hold to my statement that it's better than a bulb suspended in the air, lacking a reflective surface above it.
If you are going to paint use flat white it reflects better (suprised me), check out hydroponic forums for info. Mylar is cheap but you will have a tough time finding a place that will sell you a little. I bought a 50 foot roll for 20 bucks at a hydroponics shop, enough to last a lifetime.
Let me clarify something, when I say paint, I mean the canopy not the bulb. Painting a bulb is dangerous. Keep in mind when using a reflective material that wrinkles are negative reflectivity and actually become absorbent. Hydroponic forums are very educational in this area.