@Si Click - That's a very good point you raise. Most of the gunk present in the inlet manifold is the result of oil vapour delivered through the crankcase ventilation. EGR gases are always dry and consist of combustion by-products, one of them being a fine dust, known better as particulate. Besides burning NOx gases, the EGR also controls the formation of these gases by depriving the engine of small quantities of atmospheric oxygen. The engine will therefore run cooler and because of these lower temps and less oxygen, the opportunity for nitrogen to combine with oxygen is reduced, meaning less NOx gases.
Deleting the EGR will have the opposite effect as the engine will run hotter due to the richer air-fuel mixture. Apart from the increased production of NOx gases and other by-products, the oil temp will also go up and so will the oil vapour that is vented back to the inlet manifold system where it will condense.