8.36 to 8.48 GB is the max file size for a DVD+R9 media, 4.38 to 4.44 for the DVD-R/+R5. This is depending on how your devices report your media's free space.
To answer your question, yes, you can compress the living snot out of footage and squeeze a longer duration on to a DVD+/-R media. Quality and beauty are both in the eyes of the beholder, and as far as DVD's are concerning, in the ears as well. Don't forget about your audio. Depending on the bitrate, duration and your aural perception of your audio, the sound will be either terrible or reasonably good.
I like no less than 192 KBPS and encode in either in straight PCM or the MainConcept MPEG-1 audio, with occaisional jaunts into Dolby encoding. The higher the bitrate you go, the more space it will take up on your DVD. It is best to not cheat too much on the audio, it is just as apparent as horrible video quality, even for a novice consumer listener.