>> As a star’s gravitational well will likely be the
deepest in the system, it is also energetically efficient to launch material on a stellar intercept
trajectory.
Quite the opposite, that's one of the most delta-v expensive trajectories to embark upon. In fact from earth it's about twice as expensive as leaving the solar system.
Really? Why? Isn't the sun moving along some path in the milky way and can't we use that to accelerate the launch of a spacecraft? It looks like Voyager 2 used the effect, at least according to this image:
Orbits are not intuitive. To head "downwards", you have to slow down your orbital velocity, which reduces the radius of the orbit. In other words you have to decelerate. When you do the maths, you actually have to decelerate more from Earth orbit to get to the sun than you do to accelerate up to solar escape velocity.
Right, so an orbit implies an amount of kinetic energy which you need to lose to lower your orbit; and losing kinetic energy in a frictionless environment requires some kind of propulsion.
Are you confusing gravity assists (unpowered) with the Oberth maneuver (powered)? You can't use a gravity assist with the Sun because it's at rest relative to the rest of the Solar system. The Sun is only ever dragging you down, whereas a gravity assist maneuver drags you around the target body. (Imagine me waving my hands a lot while you read this.) You can kind of think of it like coming up from behind a planet relative to it's motion around a star, which will will accelerate you, or going in front of it, which will slow you down.
For interstellar trajectories you can use stars for gravity assists, but I'm not sure that would work for escaping the Sun. There, you would want to use the Oberth maneuver, where you get into an elliptical orbit around the sun and then fire your engines at perihelion to raise your orbit to a parabolic or hyperbolic trajectory.
In any case the Voyagers both used gravity assists around the gas giants (Voyager 2 used all four, while Voyager 1 just used Jupiter and Saturn because NASA decided to swing past Titan and didn't have enough propellant left to resume the Grand Tour course).
Quite the opposite, that's one of the most delta-v expensive trajectories to embark upon. In fact from earth it's about twice as expensive as leaving the solar system.