IMHO, a full, practical re-test isn't necessary.
It would be next-to-useless for weeding out young and reckless drivers, simply because the young and reckless know exactly what they should be doing, but they just don't do it. Cue an examiner sitting beside them, and their driving would instantly become impeccable.
As for drivers over 70, I think that simply a hazard perception test would be sufficient, and only then if the GP thinks it necessary. The trouble with the current system is that GPs will often pass older people as fit to drive because we have a black-and-white system - your GP says either you're fit to drive or you're not.