Examine the resulting dvd video with MediaInfo (free tool to find out specifications of video). This should tell you the bitrate used in making it. There are several different views available in MediaInfo...try several if you want to see what all it can tell you. Most dvd video will have between 4000kbps and 8000kbps bitrate. When I use Procoder to convert avi or mpeg4 to dvd-video, I normally shoot for an average of 6000kbps on the video plus whatever is needed for the ac3 audio.
To change/find out bitrate that Nero Vision is using you'll have to get into the settings. Been too long since I used Nero Vision to tell you how to do that.
Edit: I see you found the settings. If the resulting dvd-video doesn't meet your expectations on quality, you should be able to adjust the settings off auto and put them on higher specifications. I use VBR (variable bitrate encoding) with max 8000, and average 6000, but I don't use Nero Vision. I'd view the first results you got...it may be fine as it is.