I think repro playfields are the way to go for SS machines that have wear beyond repair. I have several repros (IPB and CPR), and these are for my Keeper pins. I will buy more as they become available. So my "line up" will have repro playfields - KISS, Fathom, Medusa, Flash Gordon and Flight2000.

For machines that don't have repros available, then the next option is to restore - but you need to rely on the restorer to make the division as to whether the playfield is economically viable. As Gav mentioned - it takes time, but it will be worth it.

When to change over ? If you have the $$, just do it.