Solid ground can be moved through at a rate of (Magic) meters per hour. This only applies to living earth, that is, soil or natural rock. The earth itself has an aura but its aura is slightly diffuse and astral forms can pass through it. Concrete or laid stone or whatever, can be passed through like nothing because it is like dead skin from the planet.
A watcher can do anything a regular spirit can, but it has no "powers" like other spirits. It's just a little astral "critter" that can do menial tasks. A watcher can manifest, but it cannot materialize, therefore, it cannot affect the physical plane. Watchers can find people by searching for them, to give messages, etc. As a watcher can manifest, it can do all sorts of annoying things like insult someone for hours on end, tail people, spy, whatever. Watchers aren't terribly tech savvy and are very bad at remembering things like numbers or math. They can remember conversations but get fuzzy with the details. They have the intellect of a loyal but stupid dog, basically. They also get confused easily if you try to give them orders with too many conditions. Essentially, treat them like Drones given a command and have them make a Force test against a target number for the complexity of those actions.
Being astral beings, watchers can attack anything on the astral plane. They usually look like a miniature version of their summoner's astral form.