2018 MARKET UPDATE: MARKET SWAMPED WITH NEW RECORD PRICES!
If you invested in House of Secrets #92 anytime in the past couple of years, then you're sitting MUCH prettier than the Swamp Thing itself.
We simply don't see this book anywhere near as often as other Bronze Age key issues.
The dark cover is really tough to find in higher grade, with only two CGC 9.8s in the census (and 20 9.6s), competition for the top grades when they come to market is fierce.
Prices are very strong, and we continue to see upside in this book's future.
2017 MARKET UPDATE:
There is no special reason for this book to be hotter this year, but it's a notoriously tough book that's under-valued in high grade. Its dark cover makes it almost impossible to find in grades of 9.0 or above.
Wrightson is only second to Neal Adams in popularity of 1970s artwork.
Bernie Wrightson is a hot comic book artist at the moment, and Swamp Thing is without doubt his finest hour.
Swamp Thing TV and Movie rumors are rife. Along with HoS92, there are two other Swamp Thing books on the Hot 100 list:
Swamp Thing #1 (classic cover by Wrightson, tough in high grade)
Saga of the Swamp Thing #37 (1st John Constantine)
House of Secrets #92 is among the most expensive 1970s comic books, especially in high grade. The dark purple cover featuring the classic "woman realizing she's not alone" image is awfully prone to wear and creasing.
Stick to VF+ or better. If you can't afford such a nice copy, wait until you can. Lower-grade examples are common, and make poor investments in our opinion.