We are installing ST springs next week so we are ready for our first autocross of the year coming up in July. Our local group (Furrin) will allow the non-ST Fiesta to autocross with the stock springs, but we were already planning on doing the ST springs regardless. I did one autocross with my 2011 Fiesta on stock springs, and I think that was the only event I ever ran with my 2011. We did run a 2009 EU Fiesta in HS, which was the picture Jalopnik used in their article about the Fiesta being banned from autocrossing.
Yes, if there wasn't an ST, I would strongly consider the 1.0L over the 1.6L. I just wish you could get better options with the 1.0L. Actually, the 1.0L should just be an option with a manual transmission in all trim levels (except ST). My brother really wanted MyFordTouch with Navigation since he travels all the time for work. I would have actually preferred to have the non-touch screen Sync from his 1.0L in my ST and he wants the MFT from the ST in his SFE. He would have gone either way on leather if it was an option on the SFE.
We are both having a lot of fun developing his 1.0L Fiesta and hope more aftermarket support comes later. The Mountune kit from Europe would really wake the car up!