This seems silly to me. Especially without a rationale to back it. Just saying.
That being said, I'm OK with the fact that usernames just can't be changed.
Wrong. 50 BTC is 50 BTC, regardless of it's value in another currency. This is a Bitcoin forum, and I sometimes don't understand when people obsess with the value in another currency. If we lower it now, then we are dishonoring everyone who has donated in the past.
I think the reason why we stick to 50 BTC is because a promise was made to donators in the past.
This maybe a bitcoin forum, but there are a lot of things which are not denominated in bitcoin, including bug bounties.
I prefer not to denominate values in any single country's currency here, but BTC is too unstable. XAU is pretty stable.