Seems I got something to work. Studying the confusing W3C SVG Links page at:
https://www.w3.org/wiki/SVG_Links
I came up with the expanded sample code for inserted images (the red is what I added):
<div style="text-align: center; padding: 0pt; margin: 0pt;">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" style="width:100%; max-width:100%; height:auto; max-height:100%;" version="1.1" viewBox="0 0 600 525" preserveAspectRatio="xMidYMid meet">
<a xlink:href="../Text/cEM03.xhtml#c0101ie" xlink:title="Click image to return to illustrations index" id="c0101">
<image width="600" height="525" xlink:href="../Images/C01Ilus01.png"/>
</a>
</svg>
</div>
It works fine in iBooks and Calibre ebook-viewer on my Mac (Apple is updating my iPad this evening so I'll have to wait to test there), including the tool tip (see xlink:title=". . ." above), though in ADE the tool tip doesn't show but the linking works.
If you have any thoughts about how this may cause issues that I haven't discovered, please speak up :-)
Thank you
PS: I understand why some don't like using an image for a clickable link, and that's why I included a tool tip. Even if a reader inadvertently clicks an image before the tool tip comes up, they're positioned in the illustration index to immediately jump back to where they were.