This is an excellent question; and is well worth discussing. To begin with, I am not sure I would call them experts. The two figures you brought up both seem to be wrong quite often. Even when they appear to be "right," I doubt their interpretation actually is correct. It is very easy to take metaphorical language from Daniel or Revelation and interpret it based on the current world situation. Personally, I don't think this makes someone an expert in anything but creativity.

Before making any interpretative moves to read Daniel and Revelation in today's context, I think we must first interpret the books in their own historical and literary contexts. When we read the apocalyptic, prophetic books in light of the communities they were addressing, we gain a much clearer picture of the way the books were meant to be understood. Why do people feel the need to read them like a newspaper depicting today's events, when they offer great insight without making such interpretive moves?

When we extract prophecy from an ancient text, and say it is about our situation, we have made a huge move that I doubt the author intended for us to make. These texts had to be relevant to the communities they addressed, because if they were not, they would not still be around. Relevancy is what made a biblical text (prior to it being biblical) popular, and encouraged the communities who received it to copy it and pass it onto future generations.

When we say the prophecies of John and Daniel are about us, we are simultaneously saying, they were not about the communities they originally addressed. Historically, I think this puts us in quite the conundrum.

Therefore, it is problematic when people attempt to read the Bible with their own logic in one hand and a newspaper in the other. I think it illustrates a common misunderstanding of prophecy and prophets which seems to present everywhere in our culture today.

I have a few posts which directly address this problem:
Prophets, Celebs and Those Who Drool Over Them
Prophets Running Wild in Society
Self-Proclaimed Prophets

So, do I think these supposed "prophetic experts" hurt the Christian message? Absolutely -- I think we get one of two responses from offering this kind of thinking to the world: (1) Man, those Christians are crazy; and (2) [The more scholastic end:] Why do Christians feel the need to interpret apocalyptic language based on today's events? And to be honest, I don't blame the people who respond this way.

I hope we can correct these stereotypes of Christians by simply reading the biblical text in light of its own historical and literary context, rather than the newspaper.