Vague Spirituality essentially pushes God out of the picture and makes him into "the big man upstairs". With Vague Spirituality, one can convince himself/herself that they don't have to worry about putting God first in their lives. His purpose is to not ask anything of you and to run in there to save the day whenever you need Him to; it's the ultimate form of wishful thinking. No longer is it about putting Him first and living a life of holiness that's made possible by Him transforming your heart-- it's about recieving a get-out-of-jail-free card by fasting and/or praying once in a while (ya know....just in case). Surah 30:33-36 of the Qur'an says "When trouble touches men, they cry to their Lord, turning back to Him in repentance: but when He gives them a taste of mercy as from Himself, behold, some of them pay part-worship to other gods beside their Lord-- (as if) to show their ingratitude for the (favours) We have bestowed on them! Then enjoy (your brief day); but soon will ye know (your folly). Or have We sent down authority to them, which points out to them the things to which they pay part-worship?".

By my count, the Qur'an mentions repentance 41 times; it's not something that's only somewhat important. Islam is about submission to God, so if you think Islam is a kin to a test-drive that you can try once to see if it reaps you any benefit and then decide if you want to be a muslim full-time, you don't understand what it means to submit to God. Part of this spiritual act is acknowledging that you need Him more than anything and that, without Him, you're lost. The day you submit is the day you give up on your own efforts and rely on Him as your source. Repentance is one of the keys to submitting yourself to The Lord; surah 25:71 says "And whoever repents and does good has truly turned to Allah with an (acceptable) conversion".