Could a designated plane spotting site benefit Stansted?
Not a chance; if anyone did suggest it it would almost certainly been shot down with the UK mantra "security is paramount"!
Security is, I'm sure, paramount across Germany, Austria, Switzerland, The Netherlands etc - but that doesn't stop them providing enthusiast facilities.
As the old saying goes, where there's a will, there's a way, trouble is there is no "will" to do anything else in the UK than fleece the punter - and your average spotter clearly isn't "fleeceable enough"