Do you ever build them? It seems to me, that they only add up to the pollution without providing any tangible benefits. Great Engineers aren`t very much needed in the late game (it`s too late for mining corp or jewelers, no good wonders). Engineer specialists provide themselves only a pathetic 2 hammers each. Even with "full emloyment" it would take about 67 turns to repay it`s cost in hammers (not taking multipliers into account). Perhaps cities with no tiles to work could use them?