To summarize:
1) How the adherents of Islam view their religion and the Koran will vary, often radically, from country to country. This is why I stated that any given religion is a product of the
time and place it finds itself in, regardless of what its holy book states or what its founder(s) proclaimed way back when.
2) Religion, strictly speaking, cannot become "secularized" --- although it may become more welcoming to secular philosophy and science (which, again, depends on the historical and cultural climate it finds itself in). Rather, I would say it is nations themselves that "secularize", meaning that the institutions of State and Religion become formally separated (by law, anyway).
3) The modern accusation that mystical lineages like Islam's Sufism, Judaism's Kabbalah, Orthodox Christianity's Hesychasm, and Catholic Christianity's Desert Wisdom traditions are in any way "envogue", "religions of the week", "trendy", "spiritualism", or even historically recent owes completely to widescale ignorance of the totality of these traditions.
I would suggest perusing the following articles:
Wikipedia: Kabbalah
Wikipedia: Sufism
Wikipedia: Hesychasm
Wikipedia: The Philokalia
Wikipedia: Theosis
The Place of Tasawwuf
in Traditional Islam
The majority of these traditions are centuries old, with Kabbalah dating as far back as the intertestamental Talmudic period, Hesychasm dating as far back as the 4th century CE, and Sufism dating as far back as the 12th century CE.
"Spiritualism", by contrast, is a modern Western movement that dates back to the 19th century CE.
4) Claiming to know what the founder(s) of a given religion did or did not teach is extremely difficult, as many religious texts are based on second-hand or word-of-mouth information. In addition, many are subject to inadequate translations and/or intentional distortion and revision of earlier texts. In any event, I'd argue the core experiences and phenomenology that originated a given religion is more important than verbal proclamations by any one person.
5) Simply arguing the "core" or "essence" of a religion is what the majority of its adherents practice is nothing short of an Appeal To Popularity and Appeal To Common Practice.
Laterz.