You can get all the Spectrum sounds on the C4. But, keep in mind the knobs are different. If you are mainly doing envelope filters, the Spectrum may be better.
This. I have both a Spectrum and a C4. The Spectrum is easier to use as an envelope filter because the native configuration of the knobs is designed to for that function. The C4 takes more tweaking to recreate that functionality. I can easily make the case for owning both, but if you are focused on an envelope filter get the Spectrum. But the Spectrum can’t use the C4’s synth presets. That’s why I use both.