The lineup barely matters for gravity assist. Jupiter is the vast majority of the total you can get. Saturn has 30% of the mass and 2/3 the orbital velocity, so adding Saturn gets you only 20% more above using Jupiter alone (and the Voyagers didn't really try), and the ice giants are smaller and slower yet.

We could easily overtake Voyager via only Jupiter if we wanted to (and New Horizons eventually will), and Jupiter-to-any-target launch windows come at least every 12 years.