The bourbon will be fine, so drink up. Unless the seal was corrupted, it will be as fresh as the day it was bottled. High-proof spirits do not change in the bottle like wine does.
Are you sure it was purchased in 1976? I've never seen a metric bottle from a bourbon distiller prior to Fall 1977, and most of them didn't start bottling metric until the early '80s, including Ancient Age (aka George T. Stagg, dba Old Prentice, Distillery), which made that one.
Collector value is subjective. There is no large collector market for bourbon, though collectors -- I'm one of them -- do exist. However, many bottlings, including yours, were made in industrial-sized production runs and are not particularly rare, even today.
As a general comparison, for example, the most recent rendition of Eagle Rare 101-proof, 10yo -- which was recently discontinued, by the way -- sold at retail for about $20. If I saw your bottle sitting on the shelf beside it, I might pay twice that, but not more.
So, if you enjoy good bourbon, it may be worth more to you to just drink it.