Were the Corinthians spiritually rich?

No, the Corinthians were not yet spiritually rich. Though Scripture says 'Now you are rich,' they were still carnal and had a long way to go. They were not yet spiritually rich like the Ephesians. Any richness they had came only by God's grace, not their own accomplishment.

Les teaches that the Corinthians were not yet spiritually rich. He notes that although the text says 'Now you are full, now you are rich,' these people were still carnal and had a long way to go. They were not yet spiritually rich like the Ephesians. This brings the whole concept of salvation back home: believers have nothing except what they received by God's grace. They cannot glory as though they had not received it, because they accomplished nothing of themselves.

1 Corinthians 4:8

Now ye are full, now ye are rich, ye have reigned as kings without us: and I would to God ye did reign, that we also might reign with you.

Were the Corinthians in 1 Corinthians 4:8 actually spiritually rich?

No. The Corinthians were not yet spiritually rich like the Ephesians. Although 1 Corinthians 4:8 states they were full and rich, the context identifies them as still carnal, with a long way to go spiritually. They had not attained that maturity.