What do you want to achieve on bass that you can’t already do?
There are plenty of bass players who can’t read music, don’t know their scales or arpeggios, or modes and still get paid.
Don’t do something because you feel you should. Do it because you want to!
Sit down and figure out your goals. If it’s to play gigs and have fun, then figure out your path to get there. If it’s to sight read complex passages, all good.
oh, and you can achieve everything you want to on a 5-string bass. Do not buy more gear.