What tools like these need is monitoring capacity. Hook your diagrams to your logs and health status, and then you have a compelling reason to actually keep them up to date.
If the diagrams had some linkage to your code you'd be able to see what a failed unit test means in the overall context of the app, what code is used in which block, what protocol is used for connections between blocks, a summary of what each block does etc...
A monitoring tool as you say - and since you'll use it often you'll probably keep it up to date