Enterprise Architects are always on the prowl for metrics which can be used to validate their existence. Given that EA is more similar to Strategic Planning and/or Audit that say Sales, IT Operations, or even Project Management, this can be a considerable challenge. Frequently, we hear that "reuse" is a measure of EA effectiveness.
We all know that reuse saves time and money, and some can even show that a strategy of reuse will improve quality and time to market. Reuse is a good thing; most of us would hold this as an axiom, but it's not a measure of architecture. Don't get me wrong, measuring reuse, assuming you could actually do it, speaks more to the effectiveness of a Shared Services Team. If the Shared Services Team is part of the EA Group, well then, I suppose it could be a sub-measure of EA. But on the whole, reuse doesn't measure the value of architecture.
Architecture is more about quality attributes such as reliability, performance, throughput, responsiveness, to some degree functionality, and cost (which implies time), all of which could be achieved without a scrap of reuse. Again, again, again, reuse is a good thing and is rightfully desired. Reusing existing components; however, doesn't mean those components are loosely coupled, properly granular, or even well-designed. But more importantly, reuse doesn't speak to the effectiveness of the EA program.
Reuse, doesn't cause the achievement of organizational flexibility, adaptability, or resiliency. Reuse doesn't indicate an alignment between the business and the technology segments of the organization. So, measure reuse because it's a good thing to do for many quantifiable and anecdotal reasons, but it doesn't express the value of a good architecture or architecture program.