The Magic of Lavos also tends to corrupt people. Lots of the Zealians were really snotty bastards... especially Queen Zeal. You don't see that corruption with Spekkio
Not ALL of them were 'snotty bastards' look at the woman who planted the seedling. I think the designers may have modeled them on the steriotypical upper class nobles of the English aristocracy. But in the same way that not ALL of them look down upon the 'commoners' (earthbounders), not ALL of the Zealians look down on other people. Most of the people in Zeal were just kind of nonchalant and lazy, if I remember. Look at Schala and Janus: both of thier hearts were in the right place at one point or another.
If you look at the Magic of the Zealians and compare it to Crono and Co. (except Magus probably) there is one major difference. Crono and Co. have Magic based on emotion. Its really unpure, unrefined, magic. The magic of the Zealians are on the other hand mastered and perfected. I think it was in the first city of zeal you go to there is a lady who says, "Your magic is so much more primitive than ours, you poor poor beings."
Who is to say that thier magic didnt become more refined after the Zeal encounter? There were higher level spells to be learnt yet, at that point of the game, and magic probably improves with practise. The Zealians had all been studying magic thier whole lives. While I do think that the Zealians had a certain detatchment from the magic and lore that they practised, I also believe that magic is constant, there is only one form of it.
It is only when you use magic in the pursuit of power that it goes wrong. Plus, the Zealians were channelling a bit of Lavos' own soul.