Will - 20 years ago Upper Vailsburg was actually somewhat on the decline as were many inner cities due to increased drug activity in the late 80's and 90's. The area is actually better now than it has been and probably among the safest in Newark. But I agree that the best bet is to visit the area different times of the day and also talk to homeowners and the police.
If you're comparing the area to the rest of Newark, it's pretty low. But compare it to the suburban towns neighboring the area, Maplewood and South Orange, and it's ok. Personally, if I was really concerned with the crime but wanted to stay in Newark, I wouldn't mess with anything North of 18th Avenue and East of Sanford Avenue (look on the map and you'll see what I'm talking about). Good luck.
There are several websites available online where you can explore crime statistics in just about every town in the country. This would be your best bet in terms of getting specific information for Upper Vailsberg. Feel free to contact me via e-mail if you have any questions regarding home values in Vailsberg.
Best of luck to you.
Marsha B. Washington