Do Religious Conversion themselves have any evidential value?

While the reasons behind religious conversions may be considered for any potential evidential value, the conversions themselves do not possess any intrinsic value apart from their rationale.

Conversions may have various motivations. There might even be a mixture of various motivations behind them. Conversions prompted by lure or coerced by means of fear or force do not possess intrinsic value. Similarly, conversions backed by diplomatic motives are neither real. Real conversions are governed by strong epistemic values of justification.

King Solomon's turning towards the religions of his non-Jewish wives by itself does not constitute an invalidation of his previous privileged claim of a personal visitation of the Lord in which he received the gift of wisdom. It does not prove that the religions that he turned to in his later years were superior or more advanced or similar to his previous faith. Similarly, King Saul's turn to spiritist involvement in the forbidden practice of contacting the dead doesn't establish spiritism in any way as a valid alternative to the prophetical movement. On the other hand, the medium's terror at seeing Samuel demonstrates the superiority of the prophetical movement. When the prophet Balaam refrained from cursing the Israelites and instead blessed them, it may have seemed that he stood in support of them. But, the New Testament reveals that his heart was covetous.

In any claims of conversions, the motives and the rationale behind them must be thoroughly investigated.

One prominent example of conversion is that of Paul. He wasn't swayed in any way by the preaching of the apostles or the testimony of Stephen's vision at his stoning. He was an uncompromising Pharisee and persecutor of Christians until he had a personal encounter with Jesus on the road to Damascus. Following this experience, he underwent several persecutions for the sake of the Gospel. There was no political, social, mainline religious, or economic benefit or advantage from this conversion. The primary rationale behind his conversion was his empirical encounter with Christ on the road to Damascus.

In modern times, we have testimonies of such dramatic conversions in people like Sadhu Sundar Singh (who came to be known as the apostle with bleeding feet), Gulshan Esther, and Karamchand Hans.

But, even as neither the testimonies of the disciples, if Paul had heard them, nor the testimony of Stephen had any evidential value for Paul, such privileged testimonies might not have any evidential value for any other person than the experiencer.

Also, Jesus said that even if a dead were raised and sent to testify, it would not be evidence enough for the Jews who did not take the testimonies of Moses and the prophets seriously. For the Ethiopian Eunuch to whom Philip preached the Gospel, a simple reading of Isaiah and a testimony of Jesus was sufficient evidence for faith.

But, obviously, for Paul, Sundar Singh (who had previously torn and burnt the Bible), and Karamchand (who previously beat his mother for professing faith in Christ) Christian preaching itself was insufficient. They were given a personal physical encounter.

Solomon too had a personal vision. But, he turned away. So, Paul places safeguards when he says: "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed." (Gal 1:8)

And, he confesses: "But I discipline my body and keep it under control, lest after preaching to others I myself should be disqualified." (1 Cor.9:27)