E-TTL vs older flash with Auto

I just bought a Nikon SB-27 to use for some strobist stuff. It has an auto mode with it's own light sensor, so you just match the F stop and ISO setting on the flash and on your camera and it works it's magic. I am surprised to find it is working as good or better than my 430EX for on camera and bounce flash, it just takes a 30 extra seconds to set up. So I guess my question is what is my 430EX giving me in ETTL that this old flash can't in AUTO? Just the ability to change settings quicker?

Those traditional auto flashes are great, within their specified parameters. They have some limitations:
1) Generally the distance scale indicates both a maximum and minimum distance for a given aperture. An E-TTL flash will let you get closer without stopping down more.
2) The sensor of an auto flash has a fixed field of view. It may be a lot wider, or a lot narrower, than the lens you're using.
3) With E-TTL you have the option of Evaluative, Average or Spot metering (with the FEL button). With traditional auto, it's average and that's it. Average works when you're indoors with fairly close backgrounds. Outdoors if your subject doesn't fill most of the frame you'll get overexposure.
4) If you get close for macro work, the sensor on an auto flash won't be pointed at your subject. This can be a real problem.
5) Traditional auto flashes have a limited number of aperture settings. With digital, you have more options because you can adjust ISO to get the aperture you want, but it's still limiting.

You can have the best of both worlds, though. The 580EX II has a traditional auto mode. By most accounts it's horribly miscalibrated but you can learn to compensate. I've used it but generally I gravitate toward E-TTL just because it requires less thought and I can concentrate on other things besides flash metering.

not sure... but just use a meter

I used auto with old Metz flashes years ago and found it very reliable. Since getting my Nissin Di866 I also use the aperture priority mode which I find more reliable than TTL.