Rahul, I think weighted average method is more scientific and gives more authentic results than FIFO method, hence more preferred in stock valuation. Others can, of course, comment if they have different views. WA method may not be appropriate in cases where items of stock differ drastically in rates per unit and weighted average will give a totally misleading picture. I do not see any other scenario where WA method should not be applied.
Even in case of jewellery stock as mentioned by you, gold rates are per gram or those of silvers in per kg; hence WA method can give authentic results according to me. However, those having practical experience in jewellery stock valuation can comment with greater authority.