What to do with old abandoned websites and domain names?

Hello all. To any webmasters, bloggers, entrepreneurs out there. I'm sure many of you have launched new projects, websites that you've worked on for a while but never took it to the next level, or grew bored of working on it and largely abandoned and neglected to nurture your website in favor of working on other things.

I have several sites and domains like that and have them in the past. Projects that I've started but ran out of steam on! And due to getting tied up in other things, not had the time to invest into them and get them off the ground! Usually these I end up flipping around the time it comes to renew them and let someone else have a go at them.

Sometimes I've seen some of my old sites that fit that scenario perfectly that I've flipped and seen the new owners put some effort into them and they have made them their money back and a profit on top and some are still up and running today. Some just eventually vanish though and that probably means they, like me, either ran out of steam or just didn't put enough effort in to take it to the next level.

And sometimes I wish I never flipped them and just kept them and worked on them myself. Because I look at those old sites and see areas on it that they should go in that they hadn't that I would of done. That sort of thing. Seeing your dreams not quite fulfilled by someone else is a strange feeling when it comes to websites. Although dream is a bit strong, more idea. But can you relate to that?

And have you ever come across this scenario before yourself for your own websites/projects? Do you have many "back burner" sites that you have on simmer? How many do you have and do you just abandon them and let them expire or do you always renew them or do you just try and flip them like I usually do on DP or WF or Flippa or somewhere?

If you keep them, and always renew them. Do you ever bring any back and revive them? Have you seen results and success from doing this? Old sites/projects/ideas you started but mostly abandoned but breathed a new lease of life into it and made it a profitable and lucrative website/business?

I ask because I have several sites like this that are coming up for renewal soon that I have largely neglected for a while and I either need to do one of several things with them.

1. Renew them and then work on them which will involve time and money.
   
2. Renew them and then just leave them as they were/are.
   
3. Let them expire/drop and just totally abandon / forget them.
   
4. List them up for sale in places and let someone else buy them.
   

With option 1, I'd have to invest time and money into them. More time than money if I do it all myself. But to save time I'd probably buy services for it = money.

With option 2, nothing would really change, I'd still have my sites/domains and everything would be as it was except how much it would cost me to renew them.

With option 3, that's more a really last resort and I hate doing that, I'd probably rather go with option 1 or 2 than let them drop as I believe in them and that wouldn't be right.

With option 4, I might be earning quick cash for them but with not much earnings or traffic to speak of offers would be low. Plus someone else would get my sites for cheap and could turn them into a huge success and that isn't right with me either lol...

What should I do here do you think?

Develop these sites and try take them to the next level & die trying?

Or not develop them and just let them die!!

Or at least try and sell them?

Which option would you say would make the most sense?

Thanks!