First, the question:

Just wanted to confirm I'm reading movement of between sectors correctly. If I move ships into a sector using a Leader (say Darth into Corellia), those ships cannot move out of the sector in that same turn because Darth (Friendly Leader) is there, correct? I couldn't move Sontir Fel to Coruscant later in the turn and call in some of the fleet/ground troops Darth had moved to Corellia?

Now the observation:

We weren't exactly sure the merits of ships. Since the only thing they 'block' is deployment on the planet at the end of a turn what real good are they? A few of the Rebel objectives require units on systems so spreading out ships is probably fastest, but unlike the slugfests that planet combats are (and their value ingame) anyone enlighten me on the use of ships besides 'we must'?

Question: Yes, you can't move ships or units from a system where there is already a leader.

Observation: I find the ships and units for the empire are search tools and power retention. So far I find the rebel ships to be defensive in nature. Trying to only strike when the time is right.

You are right about movement.

For Imperials, the ships help you scout out the rebel base much quicker since you can only draw so many probe cards a turn. Plus they let you destroy the rebel base. Plus you need a lot of them since you are not positive where the rebel base will be. They also help your economy as you subjugate systems.

For Rebels, you need to obtain objectives, slow down Imperial scouting/deployment and defend your base.

You also need the ships to move the ground troops.

There's sort of a rock paper scissors element almost. Roughly...

Ground units are needed to find/protect the rebel base. But lose to death stars

Structures beat capital ships but lose to ground units

Starfighters beat/defend death stars but lose to capital ships.

Capital ships beat starfighters but lose to structures.

Death stars beat ground defenses and capital ships but lose to starfighters.

Remember that fleets also block using the build icons as well as stopping deployment... [RR p.03: "A player cannot use a system's resource icons to build if his opponent has a unit in the system"]