It can be easy to overthink backup. I have no delusions that my work will someday have great value. My goal is to preserve my images for the rest of my life. After I am gone, it is unlikely my daughter will want to sort through tens of thousands of images to find a few keepers. My longer term archival goal is to create curated collections of prints of family and special places to be left behind. I suspect my slides and negatives will be forgotten in a closet until eventually thrown away.
As for file format incompatibility, both JPEG and TIFF are well-established and will be around for decades. JPEG has even outlived improved formats such as JPEG2000 which were supposed to replace it. If for some reason one of these formats is abandoned, I can easily export the files to a new format. I long ago converted my odd-ball formats to JPEG and TIFF files (.sfw, flashpix, .pcd, etc). I do have one PhotoCD. A few years ago I wanted to copy the images at maximum resolution and ended up having a resurrect an old computer to accomplish the task. The key to digital preservation is to keep up with technological changes. My floppies and ZIP disks are fairly useless now.