No, thousands of dollars is not necessary but could be a wish/choice, yeah? I don’t think brides splurge on dresses because they feel it’s absolutely a necessity to buy an expensive dress but rather that’s probably their taste and choice. Just like the medium-lower class in Pakistan shops at Tariq Road while the elite choose to go to designer outlets to buy clothes, even the casual ones. That’s not because it’s necessary for them to do so but they just have an expensive taste 
And exactly how many people do you know who have sold their gold jewelry to help the poor? Normally from what I have seen, the gold just sits in the lockers as well (just like the dress in the closet) and either worn very few times or passed onto the children.
And for those saying how a 20,000-50,000 rupees outfit is so NOT expensive but a $2k-$5k one is, well newsflash, there are LOTS AND LOTS of poor people in Pakistan who cannot even afford to eat twice a day.. so even if you’re investing ‘only’ 20,000 in your dress, it’s still too expensive for many people just like how $5k is too much to you. So if we apply the same logic as you are, shouldn’t you have donated that money to the poor and needy as well? After all there are simple outfits around for even 1000 rupees 
Easier to talk than do I say.