How often do you see a complete unopened box of any series of Wacky Packages these days? If it's truly an unopened box from 1974, the price is probably reasonable even with the water damage because other than an uncut sheet, it's the purest form available. Shame on any of you who would open the packs!
I think it should have a higher value than buying an empty box and then buying 48 unopened packs and putting them into it over time - or even buying 48 wrappers, 96 stickers, 48 checklists, and 48 stale pieces of gum, and resealing them to make your own packs to fill it. Sure you'd have a full box of "unopened" packs, but you still wouldn't have an unopened box from 1974. Compare that to finding a 1929 Ford Model A Deluxe Roadster in working condition, although a little dirty, with all original parts vs. buying one from the junk yard and piecing together all the missing and broken parts to make a running car. The latter might be more fun if you're into that, but the former would surely be worth more.
Too many people think that the sum of the parts is greater than the whole, when in some cases, the opposite is true when it's truly a rare find.