What are the best ways to make use of surges of traffic like this?

Getting 250,000+ hits helps with search ranking, but I don’t run ads, so it doesn’t translate directly into revenue. It’d make sense to use it to grow a mailing list for future projects, but traffic from link aggregators converts 90% worse than normal referral / search traffic. So I have two questions:

1. What do you do when one of your sites does well on HN / Reddit / Producthunt?

2. Is there any way to improve the abysmal optin rate that usually goes along with link aggregator traffic?

Thanks!