The Dr. Scientist spectrum analyzer... it doesn't really do anything for your sound but it sure does look cool.
https://www.prymaxe.com/collections/dr-scientist-sounds/products/dr-scientist-sounds-spectrum-analyzer?variant=22886665025 (https://www.prymaxe.com/collections/dr-scientist-sounds/products/dr-scientist-sounds-spectrum-analyzer?variant=22886665025)
I'm a bit of noob to DIY pedal effects but surely this cannot be that difficult to build. Any experts out there willing to help?
Not difficult to build but IC based so a knowledge of programming is required, have a google for arduino spectrum analyser, pretty easy to follow tutorials.
Before cheap computer power, spectrum analysis was not cheap to do. Without either an ASIC or some grunty microprocessor (and someone else to code it), I'd never consider touching this project.
Banggood have a few kits as well
http://www.banggood.com/LED-Music-Spectrum-Electronic-DIY-LED-Flash-Kit-1211FFT-p-979747.html
http://www.banggood.com/DIY-AS1424-Music-Spectrum-LED-Flashing-Kit-TOP-Audio-Spectrum-p-984932.html
http://www.banggood.com/With-Housing-DIY-Music-Spectrum-LED-Flash-Kit-DIY-Amplifier-Speaker-Kit-p-986043.html