Sheffield's problems included subsidence. Even the biggest airports can be affected, for example Burtonwood was the largest US base in Europe. A forty years plus career in aviation at a variety of airports leads me to disagree with your 100+ seating capacity remark......regional airport success for the business community pax depends on frequency and connectivity. As for the runway extension, it will be practically useless without a major upgrade in landing aid and associated lighting.....and the LDA is not being increased anyway. Even now there is still the comical circling approach due lack of Regulated airspace.