Using Altera Max II Internal Oscillator
The Oscillator

So the truncated "clock:" line in my second image in the question was for the output of the oscillator. Turns out that when it's forced unknown (the hatching) it stays that way, though if you hook it up to an output then that output changes as expected:





The LED Output

The reason the LED output in the original wasn't working was that I'd not hooked it up correctly. As (τεκ)[https://electronics.stackexchange.com/users/6127/%cf%84%ce%b5%ce%ba] pointed out, the divider's reset needed to be held low for it to work, and because I hadn't read the datasheet and made an assumption, I hadn't realised that CLKA only drives QA, CLKB on the other hand drives QB and QC, with QC being half a 2:1 reduction of the former. So this circuit:



Produces a much more satisfying (albeit still super fast) output which has a 60:1 reduction: