I would expect hard drives to be good for a couple of decades. IDE has been around for nearly 25 years, and can still be read. The newest machines may need a PCI card for a PATA drive, so if you have data on such drives, it needs to be migrated to SATA before PATA cards become unavailable.
Capacity grows fast enough that you can probably fit your entire career minus the last five years in the same space as the last five years.
You can usually get the informational value into an accessible format; e.g. schematics can be printed to PostScript. This may still require a lot of work to get it into a useful format, but that's better than losing it altogether.
Personally, if I couldn't transfer the data into a usable format, I'd just delete it. Either I know that I have it, or I know that I don't have it, but there's no self-deception of thinking that I have it when, for all practical purposes, I don't.
The format issue is a bigger problem than the media. If you can afford to pay, you can get files recovered from just about any media. Making use of the files is a different matter.