In the 1950s, the truly voluptuous Cadillac Eldorados were the 1957 and 1958 models, which now sell for a fortune.  No contemporary equivalents.

In the 1960s, surely the ultimate shape was the Studebaker Avanti (later the degraded Avanti II), or perhaps the 1965 Buick Riviera.  Again, no contemporary equivalents.

In the 1970s, a 1974 Firebird Esprit - really???  Surely, the 1970-73 Trans Am, or perhaps the 1971-73 'boattail' Buick Riviera.  (Seeing a pattern here?)  By comparison, the current Camaro is so ugly is ranks as the ultimate automotive anti-aphrodisiac.

Of course, just about any Ferrari will do.  As will just about any Rolls-Royce Corniche.  But surely the only BMW that merits consideration as erotic is the Z08, and that's a stretch.  We won't get into the stratosphere of the original Mercedes 300SL, etc.  Just sayin' ...