A few people have been discussing this, with the upcoming increase in min. cores for the higher performing CPU clients
This trend is likely to continue in the future, from 16 cores upwards, so having a scaleable work environment could be more future proof in terms of adding 'new' cores in the future.
And when including bonus points for quick unit return, one cluster of two (+) computers might perform better than the sum of their parts if they're working on one unit together.
So, lets compare notes/research here, post any links we can find on the subject, and discuss possible setups etc. I personally am very interested in this subject for my first dedicated rig, buying lower priced/older hardware and putting them together could be a frugal way of building a great rig.