I wonder if airshows even cover the running costs of The Fighter Collection; certainly the capital cost in terms of the aeroplanes and their restoration must be seen as an investment by the owner. And one that he shares with all of us who go to the airshows; much better than an Old Master hanging on a dingy wall and only appreciated by its current owner and his chums...
I'm pretty certain that most of the Spitfires and Hurricanes around contain at least some original material. The older BoBMF Hurricane LF363 had a serious accident and fire at Wittering a few years back and has arisen, Phoenix-like, from the ashes. How much of the original remains? Dunno.... Spitfires such as P7350, AB910 and MH434 are probably mostly original structurally-wise as they've been mostly well looked after over the years. The ones recovered from airfield gates, Kibbutzes and Orstralian desert are rather less original I'd suggest, but expertly rebuilt none the less.