Don't throw your TKD away its a pretty good long range art.
The choice of Ninjitsu or Jujitsu depends on what you want to learn to do?
If you want to enhance your locking, throwing and grappling skills Jujitsu, Some trad JJ dojos do teach weapons at a later date.
If you want to enhance your long range skills with weapontry and deception, if you want to learn to maim and disfigure and the use of Trad weapons along with entertwining the use of locks, chokes, throws and some grappling Ninjitsu.
Jujitsu is probably more practical, not that Ninjitsu isn't but it covers alot of grounds and information not practical in modern everyday life.
Depends on what you want to do, enhance what you know with closer in methods or enhance what you know with weapontry and closer methods. Ninjitsu changes the way you think along with changing your range of fighting applications.
JJ is more Practical imho.