According to David Barrett et al, editors of the "World Christian Encyclopedia: A comparative survey of churches and religions - AD 30 to 2200," there are 19 major world religions which are subdivided into a total of 270 large religious groups, and many smaller ones. 34,000 separate Christian groups have been identified in the world. "Over half of them are independent churches that are not interested in linking with the big denominations."
Looking at that long list of religions that you feel I should listen to, I notice you didn't mention scientology, the Norse religion or those who follow the gods of Egypt (to name a very small percentage of what is out there).
Are these too young or too old? How do we know which to devote our time to ... there are 1000+ religions? Do we have to give each an equal slice of time??
Well the young ones are the ones that are the most easily dismissed. For example, Mormonism claims that the American Indians are the sons of Abraham. Well, simple DNA testing has dispelled this rather quickly. They also claimed that black people are an inferior race. They sort of recanted "God's will" in the '60s. Scientology can be easily traced back to a hack science fiction writer who made up a cult based on a bar bet. Other, older religions are harder to discount just because they're older.