I also tend to hoard links. If there's a great thread on Haskell, for example, I'll bookmark it (save it to Pocket), with the intention of going back to the thread if/when in the future I decide to learn Haskell.
Ultimately, though, the problem is that whether or not I pay for this depends on whether this tool actually weans me off HN. If the summaries are so high quality as to get me off HN (except to post comments myself), I would pay $50 a month for this. If I still find myself reading threads by myself on HN, I wouldn't pay anything.
To your point on hoarding links, a comment came through from the form that they would like to see tagging functionality. I wonder if there's something there?
On gauging the quality of the service, I've included a sample digest on the site which I hope helps. However I take your point. People may well want to see that the level of quality is sustained.
(the summaries are automatically generated)
edit: "free" in the sense that I do not pay anything. However, there usually is a sponsored ad (obviously geared towards the HN community) with the weekly email.
With the Hacker Newsletter, if I don't get it sometimes, I don't really care, since it's free. However, if I were paying for a service I might feel different about it.
I wouldn't mind trying it, but I don't think I'd pay for it. But, who knows, others might! Good luck to you.
asking people what they would pay is so weak in the age of the internet and stripe.