Here's what I ended up with:

\define excerptify(title)
  <$wikify name=wikitext text={{$title$}}>
    <$text text={{{ [<wikitext>split[]first[200]join[]] }}} />...
  </$wikify>
\end

\define linkDisplay(title, filterFragment)
$title$:

<ul>
<$list filter="[all[current]$filterFragment$]">
  <li>
    <$link to=<<currentTiddler>>><<currentTiddler>></$link>: <$macrocall $name=excerptify title={{!!title}}/>
  </li>
</$list>
</ul>
\end

<<linkDisplay "Links" "links[]">>
<<linkDisplay "Backlinks" "backlinks[]">>

You might notice that if the first line is shorter than 200 characters, the lines are run together. This is a common issue with excerpting algorithms which you'll often see even on professional blogs and websites. While it's undoubtedly possible to fix, we won't get into the necessary machinations here; feel free to take it on as a challenge project if you like!