Question

Is Reagan speech a trustworthy Source about the effects of Reaganomics

Answer 1

Yes it is a trustworthy source

Answer 2

No, it is not,  A speech by Reagan is a biased source, The speech would attempt to cast Reaganomics in glowing terms. It would be better to look at economic indicators such as the unemployment rate, the GNP and GDP as well as the stock market, housing starts, economic index, etc.