yes – just a list of links should be fine. Not sure if it adds much value but you can tell ‘google’ its a Navigation element by wrapping it in <nav> tags. eg.
The TOC is an important aspect for SEO, and your remarks would be very useful for non-developers –
Is there any other functions (including SEO) that the Table of Contents Plus plugin adds (besides the styling) which we can incorporate in the lines of the code which you have pasted above so that we manage without using the plugin?