Mike....you simply don't see the implications buried in that sort of argument. The point you make: "Because you have not found it...doesn't mean it isn't there" also implies directly "it also means it might NOT be there."
You are essentially asking folks to "believe in order to believe".
Having an "open mind" in this context is just a euphemism for "not questioning". A **TRULY** open mind always considers all possibilities, and in doing so sees the weaknesses in assertions about metaphysical claims.
   Remember...*you* are making a claim....which requires you to defend it. It does NOT require others to prove it false.

If I were to make a claim that my house was built by spirits and has ghosts roaming its rooms, you'd see the point easily! You'd shrug and ask me to show you some evidence....and probably just say, "well, go on...believe as you please, but I've walked about your house, and I saw nothing." I doubt that my asking you to 'try harder' would impress you.

If I reply that these spirits have important & meaningful messages, you could rightfully reply, "yes, but I get MY messages from a different spiritual source".

well....you see how it goes. You had a strong experience at one time, and it helps you and supports you, and that's great. We're just not all 'wired' to see truth the same way.