There is a third party platform that can do this for you already. It's called Azuqua and allows you to synchronize data across all apps including MS Dynamics and not just SFDC. In the Azuqua dashboard and workflow builder you can see the sync errors that are happening between Marketo and MS Dynamics real time - you can even setup triggers to notify you of the sync errors via Slack or email.
That is a great suggestion. We are in the process of designing a SFDC dashboard (somewhat similar to the one we have for Dynamics sync) that will (amongst other things) display a list of sync errors.
Yes - your feedback largely mirrors our current thinking behind ways to improve SFDC sync (amongst other areas). We are working on some of those now, starting with the SFDC dashboard.