I've been keeping quiet about this cos I fucked up a few days ago and ruined something for someone (sorry). I swear there are no spoilers in the rest of this post

There's a ton of value in seeing something with fresh eyes for the first time.
A good story is a good story whether a plot point was spoiled or not, I get that. But the experience is different. The reason why people care about not getting spoiled is because you lose that initial experience with the story when you don't know what's going to happen whereas you can always re-read/re-watch something and experience it the same way you would if you got spoiled.
Let's look at it this way...
Experience A - no spoilers
Experience B - spoilers
You can only have experience A once whereas you can have experience B multiple times. Having something spoiled for you means you don't get to have experience A. Or you experience it in a different (perhaps lesser) way.
Now, there have been one or two times when a major plot point was spoiled for me and I recognise that the experience was totally different than if I didn't get spoiled... and I kinda liked it. One of these is a tv show where I found out that a certain character dies but I didn't know when he was going to die. So for several episodes I keep thinking "shit, is he gonna die now?" And I was on the edge of my seat for several episodes because of that whereas I might've been just "yeah, okay cool" if I didn't know beforehand what was going to happen.*
That's a rare instance though. A lot of spoilers are very specific and you know when something will happen. For the most part, I would rather see something with fresh eyes but that's not always possible.
One thing I do to counter the crappy feeling from getting spoiled is to get my wife to watch it (luckily we mostly have the same tastes in what we watch) and see how she reacts to it. So I'm kinda experiencing things through her eyes. I'm guessing it's a little like when parents don't dig on something but they eventually find a certain fondness for it because their kids love it. For example, I've heard a few people say this about the Fantastic Four movies.
Hi Vince
*I'm guessing this is sometimes why writers will tell you in advance of a character's death. Because they want to give you a slightly different experience. But in those instances, it's their choice to do it. They want you to consume a story that way. Spoilers aren't usually how they'd prefer you to experience a story.