I think it depends also on how highly you value Silver.

If you do, it'll probably be more efficient to book PE as a holiday. You'll get 90TP per TATL leg, doubled if you are eligible for the current offer - so potentially 360TP vs 80-140 in economy ( again assuming holiday offer), plus whatever you'd earn for the connecting flights at either end. Works out about £1.10-£1.30 per additional TP and a more comfortable journey (plus extra Avios)

Examples below ( with bigger "discount" for PE )