Regarding realistic terrains, I assume you are talking about the general shape of it, not the texture. I find Vue terrains not very realistic. That's why I purchased GeoControl. Not very expensive (59 euros). That tool generates the most incredible terrains. And the new version they have now in Beta is just fantastic. If you take a look at my gallery, almost all my terrains in the last few months are made with Geocontrol.

http://www.cajomi.de/GeoControl/geocontrol.htm
Another thing I do often with terrains inside Vue is create several. Instead of having one scene with just one big terrain, it's much more flexible to have several terrains. It becomes much more flexible if you want to adjust things later for optimum look (and, believe me, you will want to adjust things a lot...). For example, to create rivers and valeys with Vue standard terrains, the best is to create several normal terrains and play with them like Lego until they fit just right.

Have fun! :-)