Higher power improves the fishfinder's ability to see small objects. I wouldn't pay much attention to power unless you are comparing two units from the same manufacturer. There is no standard for measuring it, and it can be hard to tell what the numbers mean.

Higher pixel count improves the fishfinder's ability to display small objects. High power is useless without the pixels to benefit from it.

Even moderate cost units can show a crappie jig in the water, so it isn't that big a deal.