Interesting debate and one that has been discussed many times, but at the end of the day it comes down to 2 things - Money and Manpower. Both are comomodities are in short supply and has to spread across the ever increasing numbers of preserved locos (both Steam and Diesel). Say a shining knight comes forward and restores 34073, 25244 and 45015, great but what happens when his money runs out or he shuffles of this mortal coil? And is the resurection of any of those 3 going to deprive volunteers from an already working member of the class?
The simple facts are circa 300 steam locos and 400 diesel locos preserved is not something thats feasible to maintain over the next 30 - 40 years. Will the rail fan of tomorrow be interested that 34073 languished in a south wales scrap yard for 30 years or 45015 is the only survining class 45 ever to have nose doors? Unlikely. Whether we like it or not some locos will be scrapped as spares run out for them or the expertise to repair them disappears. The availablilty of space for all these preserved locos is fast disappearing with many lines saying "full" or at least only entertaining locos in running order with a full support crew to maintain them.
Although as my ID suggestes I like them, we have reached saturation point with the amount of preserved class 37 (circa 50) with locos in near working order going for scrap with it seems anyone who wants one has got one. The arguement could be said to be the same with the bullied pacifics which are hindered by their size, coal consumption etc hence why 34073 has laid unrestored for many years.