When I was manually doing “This Day on Stacker News” I was zapping all of top posts and comments. 

Some of the issues you mentioned might smooth out as we have more time with LIT. Comments may become more spread out over time for instance.

Undisciplined

I think most of us would like old threads to come back to life. We just aren't sure how to do it well.

Excellent points. 
I've deleted replies on "necro'd" old posts on SN after noticing the date of the original only after replying. 
I suppose that's bacause of having been potty trained on old school forums where bumping old threads was frowned upon.

unboiled

Maybe some of this is fixed if the person who zaps it back to the front page also leaves a comment (under LIT, this comment should be at the top). I've tried this a few times, but it doesn't seem to work too well.

When LIT first came out, I tried zapping interesting posts from "This Day on SN" and also tried leaving fresh comments on them. Even though many of this was dredging up pretty awesome old posts from SN's archive, I did not succeed in getting a conversation going.

I had thought it would be cool if the "This Day on SN" bot actually just zapped the top post from each day in previous years, but I don't know that people want to see that much old content on the front page.

lightning

An observation on SN.

Aardvark

There are also so other problems:

1. the date is shown. This makes it feel old and even if it is on the front page, people may not want to click on it because recency/novelty bias is so strong online.

2. old comments dominate replies. if you do click into the post, the most recent comment may be from a long time ago. This makes you feel like it's a dead conversation. It doesn't feel like there is a starting place. 

3. as a reader, you don't know if anyone is going to interact with you. as you point out, the OP may not even be active on SN any more. Making a comment may be like throwing words into the wind.

Maybe some of this is fixed if the person who zaps it back to the front page also leaves a comment (under LIT, this comment should be at the top). I've tried this a few times, but it doesn't seem to work too well.

When LIT first came out, I tried zapping interesting posts from "This Day on SN" and also tried leaving fresh comments on them. Even though many of this was dredging up pretty awesome old posts from SN's archive, I did not succeed in getting a conversation going. 

I had thought it would be cool if the "This Day on SN" bot actually just zapped the top post from each day in previous years, but I don't know that people want to see that much old content on the front page.