From 1st January 1985 the USD lost 64.13% of its purchasing power (according to BLS CPI) ; At the same time the nominal value of SPX index rose by 1594.95%
Adjusted for CPI and dollar purchasing power loss, the real rise in the SPX is only 507.40% ; In other words, the SPX index price would have been $1372.41 right now if the USD kept the same value as it had on 1st of January 1985.