I don't own one but I've see what they do to the soil below.
Yes, the water is 'dispersed' but it STILL falls in great quantity. The water splashing on the ground 'softens' the soil and as the rainwater drains away, it erodes the soil. Also, it splashes a lot of dirt up onto the house, or whatever, they're installed on.
As for 'fixing' your current gutter problem, if you eventually go w/new gutters, get seamless gutters. (They're bent-and-folded from sheet-aluminum, usually on-site. Hence, no seams.) Make sure you have drip edge under the first course of shingles too.