I love Walking Dead. I was an early adopter. My collection ran back to issue #1 of buying it off the stands. I've bought and read every issue since. All that being said, take a breath.
#4 should scare the living mess out of you if you are concerned with long term growth. Spikes beget spikes in the inverse.
As for "generations to come"....do you know a lot of people that want "Whiz Comics" right now? That comic was one of the original juggernauts, selling nearly 1.4 million copies PER ISSUE at its peak...and was GONE within a decade of those sales figures.
That was our parents and grandparents generation. Do you see anyone outside of a few GA collectors who gave a hairy rat's about Whiz? If they did, and if current success was a guarantee of future quality, sales and popularity, Captain Marvel would be the biggest book going today. Books come, they go, no matter how popular or hot or great, tastes change, trends change, nothing lasts forever. Marketing, support, and fresh stories are integral to success. There's no guarantee WD will have any of those three for any guaranteed period of time.
Have a little perspective.
Maybe I should get both my #1's graded and sell them to get a Amazing Fantasy 15.
One's got a 50 year track record of demand and is a multi-billion dollar empire appealing to small children as well as it does to adults, and has a marketing team that has products and items in every category and in almost every possible retail location all over the globe with no end in sight, the other (while currently popular with a TV series buoying interest and prices)....somewhat less.
There's devotion and then there's blind devotion. I find it much easier to enjoy comics with my eyes open.
Yeah I am really starting to think about getting all my Image #1's graded and sell them. Using the profits to get me a nice Graded Amazing Fantasy 15. I remember years ago I was going to get one for $6,500, 6.5 graded blue label, and I told my wife. She got pissed at me and gave me . I showed her what 1 at that grade is worth now, and she like when do you ever listen to me.