See, I actually think Spiner is ok as Lore, because Lore is an over the top kind of character. The idea was that Lore is the opposite of Data. Soong was making an android that had better than human characteristics, better strength/durability, better brain capacity, better eyesight/hearing etc... He ended up making Lore's emotions more potent than a human's as well, and as a result, made emotions that presented as a complete psychopath. He's written to be unstably overplayed, as evidenced in his drastic mood changes in BrothersIndeed. Data's Day and In Theory are great examples of how to do a different kind of Data story and give Spiner an effective showcase.
I think they got it into their head that Spiner was some kind of brilliant actor. He's wonderful as Data because it forces him to focus and prevents him from going big with his comic acting. He can be very good, but his natural inclinations are always towards the big and the melodramatic.
As Lore he becomes a scenery-chewing, moustache-twirling villain, when the part probably called for a more subtle, sinister portrayal. But I suppose it sort of plays into the character, because Lore always turns out to be totally inept with stupid plans which make no sense. No wonder Soong took him apart.
It may be the only time Spiner's rather hammy customary acting style actually works. Any time else that they let him loose, Fistful of Data's, Masks, etc... he's painfully lame. He's even a bit too hammy in Power Play, Whereas Meaney & Sirtis nail that episode