wattage

20000k sounds a bit high to me. In one aquarium I'm using GE 6500k T-12 bulbs from wal-mart that are doing me well. In another aquarium I have a quantum aquatics 7000k daylight t-6 that fits in the standard t-8 / t-12 fixture and fires with an electronic ballast. I probably wouldn't trust a magnetic ballast to fire that one. This aquarium does look brighter than my other. Both aquariums are around 1.5 wpg. With that being said the first aquarium has more driftwood and a darker backdrop and has an overall more subdued look to it. I do like the colors that neon tetra and harlequin raspborra developed in the aquarium however. I'm not sure if any of this helps you any, but it is important to remember that different bulbs labelled the same spectrum will give you different looks. If you buy one you don't like the look of you can always take it back and try another brand.

Switching bulbs won't improve plant growth but it may make things look better. The sunglo has a higher lumen rating so things will appear much brighter. It should also give off more light in the green wavelength, making your plants look greener.

If your plants aren't growing well, other things are likely involved like nutrient deficiency or lack of CO2. May also depend on the plant, some do require more than 2wpg to grow.

The sunglo won't make some colors, reds and blues, stand out as much as the powerglo but it won't wash out the color like a lower k rated (below 5000k) bulb would.

Are these powerglo bulbs sold at Walmart of Home Depot?