I've seen the Rebels load up on Mon Calamari cruisers too often to ignore the need for a Super Star Destroyer. It would have been a handy deal breaker for me during those confrontations because even with some capital ship and fighter superiority I've had trouble with big fleet engagements, and it plays right into their hands. Of course it behooves the Imperial player to have a Superlaser Online.

The Rebels have had an edge in the games I've played in since they can meet objectives in different ways depending on the board setup. Infiltration is a must early in the game to cycle for more feasible objectives, and given all the Empire wants to do in the first few turns there's a chance the missions could go unopposed and hopefully without the risk of capture. The Empire has a lot to balance early on for actions since the player will probably want to do some R&D and move at least one fleet, and this is part of the challenge for playing the Empire since the player must maximize action economy. I've seen Rebel victories where their fleet is wiped out early in the game but thanks to widespread diplomacy, well drawn objectives and a relocation they were able to hold out. Conversely, they've also won amassing large fleets of cruisers forcing the Empire into an unfavorable confrontation.

With Rogue One coming out I think one could backtrack the setup of the game to approximate the conditions of the movie. The Empire starts out with a Death Star Under Construction at a remote system of its choosing with the Death Star on the 3rd slot of the build queue. To reflect it's fledgling status before it's "first victory" mentioned in ANH, the Rebels start with the Reputation Marker on 16. Each faction only starts with two leaders (Vader & Emperor, Mon Mothma & Dodonna), with the other starters coming one turn at a time - in essence this is like rolling back the start of the game two turns (like what is done in modifications of Axis & Allies to reflect 1939, 1940, etc scenarios). The Empire could begin with one more subjugated system in addition to the starting three but the same number of units, making them thinner at the start, while the Rebels could be allowed to spread out their starting units more to strike vulnerable systems. It gives the Empire two more turns to consolidate and look for the base at the expense of waiting for the Death Star to be operational while the Rebels can still get started with their objectives and try to peel those Death Star Plans as soon as possible. Just spitballing a bit, this would definitely need to be playtested.

Cycling the objective deck is critical, since you it allows you to tailor your strategy to the starting conditions. Goes without saying you'll need the Death Star Plans as soon as possible. You should be able to get early Infiltrations in, which should go unopposed by a small Imperial leader pool (Vader could always attempt a capture but it's one fewer move for the Empire). I agree that there can be diminishing returns to early Sabotages since the Imperial player should be playing R&D early on to get a Superlaser Online or a SSD. By midgame projects are not nearly as useful because of the lead time for big projects, so Sabotaging is doubly effective as a way to stall the Empire. One thing I've found is the Rebels can win in many different ways: last week I won as the Rebels despite no fleet presence after an ill-fated attack on a Star Destroyer but a heavy emphasis and then lost as the Empire later when the Rebels amassed a big enough fleet to take on my forces despite being cornered and having limited popular support. I also like to start with a small force in a neutral system to get a head start on diplomacy.