If you use synthetic ester-based oil in a relatively new petrol engine, top it up regularly, and the engine runs very quietly and basically without any noise whatsoever (especially after another top up), and can easily go up the minor hills without having to go into a lower gear (with automatic transmission), do you actually still need to do full oil changes at all?
Consider that it doesn't appear to be uncommon or even worrisome for the oil consumption to be around 3k to 6k miles per litre or quart, which means that every 12k to 24k miles, you end up with about 4 litres or quarts of new oil in the engine, leaving only about 2 litres of old oil still in the system after a year or two.
From personal experience, I'm currently running my 2008 Jetta SE 2.5L 5W40 with about 6 litres of top ups (~1L Castrol, 1L Petrosin, then after learning about ester-based oil, 4x ~1L of Red Line Synthetic Oil (or perhaps even 5x)), which basically means that there is almost no original oil left in the system.
The last oil change was done at a dealership in November 2010 at ~29k miles; it's now September 2014 and ~68k miles (68k − 29k miles, ÷ 5,7L, ends up about 7k miles per litre of oil); after the most recent top up a few weeks ago, the engine runs very-very quietly, and I'm still getting excellent mpg after doing these topups, and the engine can currently easily handle modest hills in the normal gear without automatically switching to a lower one up (I've noticed that going up the hills was a problem when the oil was low (at the point of needing topup) and prior to adding the 5th top-up, but it wasn't even a problem when I was about to add my last 6th one up, probably because I'm now all Redline and also it wasn't below the recommended minimum this time around).
I plan to finally do an oil change soon, myself at a DIY shop; is there anything I should look for or be familiar with when trying to do an oil change at such an irregular interval? It'll be 100% Red Line Synthetic Oil, of course. I'll probably buy an OEM oil filter from the dealer.