Actually, it's not good news for the low level routes at all unfortuantely. This exercise likely won't send any aircraft into those areas (and they are in the minority as far as low level areas go) where photographers can position themselves like the 'mach loop' or the other well known areas.
There's also a chance it could mean that those areas see less action because of the exclusion zones set out by this exercise, but since I don't know the geography of Wales I couldn't say where as I don't know where this is taking place. I'm not saying this is the fact, but that's how these things have often tended to work in the past. Nice gesture though.