Yep,, when I go to Vietnam I use Hanoi as a base. The far north west is drop dead beautiful, especially around Lao Cai and Sa Pa. Halong Bay is special also.
For me, anywhere south of Hue and Hoi An isn't worth seeing.
Depends on the purpose of the trip. Saigon was definitely better for drinking and bar hopping. Hanoi was awesome for culture photography.