Short answer- ‘need’ is a strong word, but your synth tracks would certainly benefit greatly from a preamp.  Simply put, adding a preamp to your synth lines will make them come through a little stronger and have more impact on the mix.  Any preamp, whether they be solid state or tube are designed to make your signal louder.

We have done some A/B testing with one of our favorite analog synths, the Korg Minilogue, and found that a preamp or external tube amp helps the synth to stand out.  It goes without saying that you will be using a wide range of synth voices so where and when a preamp adds the most will vary. 

This Allen & Heath GS3 - currently in use in the studio - is an analog mixing console from the mid-90s.

When we received our Allen & Heath GS3, it was caked in dust but otherwise in great working condition. We wanted it to sparkle like the technological marvel it was when it was released in 1994, so we took it apart and gave it a deep clean.