I'm not sure if anyone has posted this idea in forums yet, but, here's my idea... With attack buildings you can have higher attack than defense, higher defense than attack, or even attack and defense... Well, with spy buildings you can't have 2 of those choices (Higher attack than defense or higher defense than attack) so I think there should be new buildings: spy buildings with higher attack then defense and spy buildings with a higher defense than attack (so you won't waste lands and hurt plunder with defense towers). This will also help with wars and OSW's (not that I'm giving any support to OSW's).
Changing the spy attack and spy defense ratios would do little to affect the outcome of an osw or most of an EE. If you are being stripped in an osw, your spies will be at zero. This means you have no spy defense coming from your spy buildings regardless of what the ratios are. In an EE, most of the war will be fought with low spies, same concept. It might be cool to have different spy buildings but not for the reasons listed by the OP.