I have never had a Spirit with the Audi engine, but I did have a Gremlin once with one, that was many years ago. I drove it in high school while I was fixing my Javelin up
I remember it got decent gas milage, was a little under powered for the weight of a Gremlin, but then again I was compairing it to my built 360 javelin!
Not sure how hard parts would be to find now days