I absolutely agree with corporate-wage-slave about lounge access and priority being worthwhile going for silver if you fly in WT/WTP alot. But I guess that's a very subjective standard.

Silver, however, also nets you 100% more avios for every flight, so you can actually calculate when the extra cost of going for silver would pay for itself.

- A WT r/t ticket LHR-IAD nets you ~7400 Avios on Bronze/Blue level.
- With Silver, you're getting ~14.800 for the same flight in the same cabin.
- For an Avios redemption WT r/t ticket, you will need 40.000 Avios
- So, With Blue/Bronze level, you need 6 flights to collect enough avios, with Silver you need 3.
- Cash-price for the flight (r/t) seems to be around 700 GBP.
- YQ and taxes amount to ~360 GBP for the same r/t trip.

So, with bronze, you get every 7th trip for roughly half the price, and with silver it's every 4th trip. Together with the 300 GBP that c-w-s indicated for a mini-TP-run, I'd wager that going for silver starts to make sense, "financially", once you make the trip to the US more than 7 times a year in WT.

That said, I still believe the other perks of being silver far outweigh the avios bonus.

Don't forget that spending your avios on WT redemption seems not to be considered as getting you the most bang for your avios-buck by many FTers. Especially with Silver UuA is very attractive, and personally I wouldn't dare using my hard-earned avios on a seat in the self-loading-cargo cabin.