Despite what anyone else says (and the extreme dispensational hermeneutic often used to justify it), I believe that 2 Chronicles 20:20, as well as all of the Old Testament promises are for the people of God today:
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:*(2 Timothy 3:16)
For all the promises of God in him are yea, and in him Amen, unto the glory of God by us.*(2 Corinthians 1:20)
Besides that, the New Testament itself gives clear instructions on what our attitude is to be concerning prophecy: "Despise not prophesyings.*Prove all things; hold fast that which is good" (1 Thessalonians 5:20, 21).