I'm not sure in what way MVC would be overrated.
Although the Moodle code is getting better there are still places where (part of) the view (AKA html code) is constructed in the code that processes a form submit.
With the renderers it becomes much easier to make a small change to the way something is displayed. But when I had to remove some icones from the standartd calander block I had to jump to a serious number of hoops to implement that.
So yes, being able to extend the model, change the flow (control) and/or the view, just by extending/overriding existing classes/renderers will make development a lot easier.
Even developing a new block could be just extendeing the base block class and renderer and adding just those bits of code you need.
I'm hopig that creating a new question type will work in that way
As mentioned before, I've been out of it a while, so not really up to speed with the latest improvements.
Anne.