No, it's not a dead end trying to sue them, even if they do have the record industry behind them. This is a point of law, and they made blatantly false allegations which were both damaging and stressful to those accused. Materially, some were undoubtably forced to divert resources and time to investigate the accusations and then prove their innocence.
The RIAA apology is unacceptable. It is clearly a made up excuse to cover up bugs in their own software, which they do not want investigated. I'd be willing to bet that there is no temp, and that there were indeed far more than the number of incidents the RIAA admitted to. Their spokesman was telling porkies. I doubt very much a court of law would view this watery excuse for an apology as suitable redress for the damage caused.
I'm waiting with baited breath for the day the RIAA and the laws they rely on are put to the test in countries where US Federal Law means jack.