I wouldn't value gold that much above silver - And as Mikeyfly says, you can spend that money next year on a holiday you actually want and requalify for silver anyway.

Valuing the tiers is a very personal decision, but I think you can maths it out...

Realistically, I look at the benefits somewhat like this...
Flounge vs Club - Maybe £30 a visit improvement? Both still have food and drinks. I think this is generous.
Gold wing vs priority security at LHR - Maybe worth £15.
Group 1 boarding - Maybe worth £2
Extra baggage - For me worth £0, I have never used it
Gold priority reward - For me worth £0, I have never used it.

So even if you do 20 returns a year, maybe £940 of additional value. And really I am not certain on the flounge vs club value. If that was only £10 then it's £540 of additional value per year. Depends how much you value champagne vs prosecco and black pudding I suppose.

The more flights you do, the higher the value, but also I expect the less time you actually want to spend in the lounge enjoying them...