IANAL, but I think you've right that you don't need to hold on to the shares, and you've pointed out the only groups of investors who would benefit from the judgement. The most benefited would be those who were harmed but sold their shares before the lawsuit was announced; shareholders who sold their shares before the matter was decided are likely to benefit to a lesser degree.

In reality, class-action lawyers go looking for class members to file suit on behalf of, and make special arrangements for them to receive additional compensation above and beyond what 'regular' class members get.