I would suggest using a counter eVar and numeric success event and passing and increment to the eVar and event on each page load for the specific pages.
You could do this in DTM or similar TMS
Alternatively you could also us processing rules which would give the business user greater control over modifying the pages that should increment the engagement event.
Considering the concept that not all pages are made equal and other interactions such as pdf download, interaction with a tool such a a loan calculator in the FSI use case a more advanced approach to engagement scoring would be to increment the numeric event by 1 for a page view, 2 for a pdf download, 3 for a calculator, 10 for an application started but not completed.
s.events="event99=1";
s.eVar99="+1";
s.events="event99=10";
s.eVar99="+10";
The eVar will help you understand which level of engagement has a higher propensity to convert for different types of conversions.
The event will help you understand which marketing channels, campaigns , internal search KWs generate higher scored engagements. (you will need to use calculated metrics to average these our per visit in order to normalise the data).
You can also trend this.
If you are looking to measure engagement scores over different temporal horizons (for example visit vs month vs lifetime) you could populate 2 eVars or more with different expiration windows.
I hope this helps.
There are a few blogs around on this and will try to add them in the comments if I can dig them out for you.