The problem with growing land out from a central seed is that the high areas tend to concentrate in the center of your land masses. On a continental scale, that just ain't necessarily the case, at least on earth. This is a typical flaw in most generated map. Another problem I see is that coastlines all have the same fractal dimension (the same amount of wiggliness). A glance at any atlas will show that, except for fairly small sections of the planet, this isn't true either.

That said, remember the old engineering maxim, "First make it work, then make it work well."

One way you might remove the directional bias in your elevation model is to use two frames. The previous iteration is used as the basis for the next, but its values are not changed. That way the new values can't bias subsequent new values. I tried this once on a project I worked on longer ago than I care to admit, and it worked out pretty well.

The seed model might be improved by encompassing a directional bias, so that one direction is more likely to be raised than another. To avoid ending up with stripes, the directional bias should probably vary from seed to seed, and change slightly from iteration to iteration. I have not tried this, so I can't promise good results.

--Hugh