Stats go up a bit, plunder goes down some (at least on the same target). Your choice on what you want.
The plunder goes up a little for troops buildings, but down for spy buildings while the stats increase a little for both.
If you mean a level 1 SoS, you're wrong. The SoS gives 2,700 more spy attack bta and 2,700 more spy defense bta than a level 4 guild, but lower plunder. For more building info, see Wulf's building and land guide. It's stickied in the strategy section.
I think you have some plunder loss when you upgrade t3 maxed to lvl 1 t4 because you become that much stronger and the ebs will be that much weaker if that makes sense lol