In my experience, a high percentage of the people who state that they "prefer" acrylic have never actually experienced silicone. FWIW, I've never heard anyone call silicone "itchy" before, and I've been doing this a long time. Silicone is stable and non-reactive, and longevity is not an issue. It doesn't shrink, nor does it lose its pliability. Even the companies who promote an all-acrylic IEM line still deliver their custom earplugs in soft silicone (though usually made by outside labs).
We have customers still using early 2X-S models they purchased over 10 years ago. I can wear my Sensaphonics silicones 8-10 hours a day without discomfort or ear fatigue.
For me personally, it's all about fit, comfort, seal, and isolation. The superior isolation lowers the noise floor, which nets an improved S/N ratio. That means accurate delivery for greater fidelity, and the ability to achieve high-impact audio at lower, safer levels. Acrylics can't be fitted beyond the second bend in the ear canal, and they don't move with the canal, which makes them much more susceptible to lost seal (and thus, lost bass). Adding extra drivers to compensate for this design flaw may be effective, but it does not promote safe listening. Quite the opposite, in fact.
I understand the whole reshell/resell culture, and how acrylic construction supports that in the consumer community. But if I'm on stage, trying to hear my monitors clearly and without interruption, hoping to have a long career as a musician (or sound engineer), I'll take silicone every time.
