Things notable about Bryce:

1. You don't need to spend extra to use USGS DEM files. Bryce will import most of those ok.
2. You can export the Bryce heightmaps to .pgm (Thus you can convert the DEMs, if desired.)
3. The Bryce terrain editor is better in some aspects. Painting an elevation doesn't screw up the rest of the map like Carrara's editor does. (Or at least it does in 6.2 and older.) So if you wanted a road going through a mountain pass or a river bed, the process is really straight-forward in comparison.
4. Bryce also has some neat tiling features for its fractal terrains. But this involves a bit of more in-depth knowledge. I won't go into much detail here, but this info isn't too hard to find. It is possible make some uber-massive and consistent landscapes this way.

Although Carrara (at least 6.2 and older) doesn't seem to import .pgm directly, you can easily convert .pgm files in 2D software to other formats. (It's just a plain ol' grayscale heightmap.) PaintShopPro works for this, and I'd assume PhotoShop and Gimp can do the job as well. (Although PhotoShop may require a plugin.) Saving that as .bmp or .png means you can import it easily enough into Carrara's terrain editor. Note that you'll have to dial in some parameters in Carrara after importing so the heighmap levels are apparent.

Alternately you can save a Bryce terrain to .obj. Bryce will also generate maps with UV texture based upon Bryce materials, so that provides some other options as well. (Like editing in a modeler to add caves or cliff ledges, etc.)

Yes there are extra workflow steps when using Bryce to complement Carrara, but don't rule it out completely.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.