20 years is more than enough
If a company can't make a decent profit from a recording in its first 20 years, it means one of two things -- either the recording is worthless (in which case it isn't going to make much in the next 30 years anyway) or it spent too much money making the recording.
These days, you can make decent recordings without needing lots of equipment, so there's no justification for having big record companies and therefore no need for the present excessively long copyright protection.