I would either invest the $400 in a new bass if I thought that spending more money would enhance the performance... which I don't personally.
Or I would work hard with the instrument I have at hand and concentrate on what really matters when it comes to producing a good sound which is your fingers.
I have a $300 mexican P-bass which I can generate the quality of sound I do on a $15,000 Fodera... it really does come mostly down to the fingers, the heart and the soul.