Is there a recommended resource for a Marketo and a Marketing Automation/Marketing Operations maturity model?

I'm pretty sure this is still the same one that Marketo are currently using - perhaps with some minor modifications. If you're looking for a more up to date version, it might be best to reach out to your local Marketo rep to see what they can provide.

The field of marketing operations isn't widespread so you won't find a lot of content about it.

Regarding your point about maximising your organisation's usage of Marketo... in most organisations, change still needs to be driven from top-down. Marketing automation, and a general focus on data quality, lifecycle marketing, content strategy and Sales + Marketing alignment needs executive sponsorship and be championed across departments, it's not just a case of 'we're the marketing team, we just implemented marketo so everyone get on board'. If you didn't have an exec sponsor before purchasing Marketo, you're going to need to go hard at championing a vision (an end state for marketing) that your execs will buy into. And just this process may take months to get buy in.