I think a term limit would do well to reduce strategic nominations and strategic retirement. However, I think it should be fairly high, with ~20 years being a reasonable amount. Something like 9 years seems too short, making judges more likely to be partisan and short-term in outlook.
That was exactly my thinking as well. For a Supreme Court set at nine Justices, a single non-renewable 18-year term for all Justices would work quite well. (And if that's the standard for the highest court, I see no reason why it shouldn't be the standard for all lower courts as well.) That'd work out to two Justices being appointed per each Presidential term. With that set in stone, you'd know you'd be voting for in terms of judicial appointments.
See Larry Sabato's
proposed amendment: