Maybe turn off erosion? After all, erosion is already a part of the heightmaps of the real world.
I count on erosion to smooth and vary the terrain of my heightmaps. Worldgen is a pretty complicated process, so I let it do as much as it can to help me.
The heightmaps I use are modified to work well with worldgen. I trace out the Oceans on a topographic map, using 2 shades of gray(#000000,#222222) to denote the abyss and continental shelves. Then I trace over the topography of the plains with 3-5 shades (Between #333333 and #777777). I add hills and mountains on top of this in the appropriate areas. I use one shade for hills (#999999), and 3 shades of mountains(#BBBBBB, #DDDDDD, #FFFFFF).
Once I have done this, I paint the river valleys on another layer with #888888 gray fading into transparency, and use color combination effects to mask this to the heightmap layer to get broad river valleys that will keep major rivers on the right course. The last thing that I do is to slap a 5 pixel gaussian blur on everything, then resize it to 257x257 and save it as an 8-bit bitmap.
In perfectworld, after importing the bitmap, you adjust the "% Below Sea Level" and "% Below Tree Level" to make sure the oceans and mountains are at the correct heights. Perfectworld will take care of assigning elevations from 0 and 400, with the standard sea level being 100, and anything over 300 being mountains (I think). I also spend a lot of time fiddling with the elevation map in perfect world to fix errors in geography.
Peaks only appear on #F mountains, and standard worldgen parameters will erode small sections of #B mountains to hills while still allowing lots of rivers to start there.
This keeps everything looking like it should, with real-life mountains and hills corresponding to their equivalents in DF.
There. Quick tutorial on making quick-and-dirty heightmaps. This makes fictional worlds much easier as well, as you can simplify the plains down to 2 or 3 levels, and bang out a heightmap in no time at all. (After I had figured out the correct shades of gray to use, it took 15 minutes to make the North America heightmap I used.)
I do all of this in Paint.Net, because it is free and makes layers easier to use than Gimp does.
Edit: Added some steps I forgot. Oops!