Fundamentally there will be more, cause when you enable physics simulation, as described Simulation every physics aspect of the game (which you will eventually use) is subject to effect your ship.
Ex:
Phsyics Sim : You hit a meteor, inertia of the impact is transferred both ship and meteor effecting their directions in space.
Without Sim : You hit a meteor, depending on collision setup
- Maybe pass through it resulting no impact calculation.
- Maybe It will collide: but it is going to ignore radial impulse cause its set so.
- Maybe it will collide but physics interaction on character is disabled making a different calculation.
So its really hard for me to say without actually counting it but Unreal performance wise (with my limited knowledge) it is pretty good already with phsyics. The thing is to how to control things gameplay wise since after all generally we are not making a simulation (some games are:) )
Using physics disables collisions.
Not sure what you mean by that, I don’t think I said something like that however if I said think I did say it wrong. Physics simulation requires collisions enabled. Besides that collision is just collision, its yes or no and ignore type of response to some other collision channels.
Depends on what you want to achieve. Generally its hand crafted functions that makes the movement good. In games we don’t want too much realism. You don’t want your awesome super duper ship to be destroyed by a tiny little meteor made out of a bizarre material. Or you don’t want to die in hardcore wow when you step to lava for a small amount of time 
Let’s take a look at this sophisticated movement. Many things going on
- There is inertia of ships movement from side to side
- Forward accaleration is effected by ship forward and lateral movement enabling player to have control over the speed.
- Strafing moves affects the velocity like there is aerodynamics, on drift it slows down.
- There is almost no gravity in effect.
All things are physics as said in the end and they can be mathematically described in some code to achieve these results.
However if we would some real phyics features to make a simulation realistic as possible (some studios call hyperrealistic) it would be hard for player to have this experience since we have to talk around, fluid dynamics, then ofcource aerodynamics, air cushioning etc, probably bunch of more that I forget. I can talk around about why more if you like but its not the question you asked so skipping those. Still if that ship while passing close to some objects camera can shake, making it realistic and immersive while not effecting gameplay.
So when its just about having a certain control about what you want to do. There is no downsides. If its fun, its fun and whatever feels good when you play the arcade ship, do that.