There is an effort to map Earth's gravity, GRACE, which has been ongoing since 2002. It's produced this:

Neat, right?
Several GRAIL-like missions are planned / in progress / completed.
- Mars Express.
- LISA, a probe designed to measure gravitational fields in space, with hopes of finding black holes.
- Magellan mapped Venus' gravitational anomalies.
- MESSENGER for Mercury
- Cassini mapping the gravity fields of Saturn and it's moons.
- GEORGE, a proposal for a probe to Uranus with one purpose being to 'characterize the gravitational field of Uranus and make a gravity map'.
As for your other question, I would say that it would certainly be nice to have such data on gravity variations, but it's not strictly necessary. We can deal with such things as we come to them with just a few thrusters and make up for what variations in trajectory are caused.