Well they knew V'ger was coming days in advance of it reaching Epsilon 9. Was nobody scanning the Narada until it reached Vulcan orbit and started drilling?
The impression I get is that with the kind of warp technology they're using in ST09, a ship at warp cannot detect what is going on around them in normal space, nor can a ship or sensor platform in normal space detect what's going on in subspace.
It seems inconsistent with previous depictions of warp drive, but, honestly, I like that idea better. It's more dramatic.
Why didn't Earth or Vulcan send out a ship to intercept after it left Klingon space and open a dialogue?
What makes you think they didn't? It's entirely possible that they did and it was blown up. It's not like the Narada's first reaction to someone trying to talk to them was to invite them over for tea and biscuits.