Unfortunately, if you want to be primarily a spellcaster, you don't want a multiclassed sorcerer. Even single-classed, the sorcerer is one level behind the curve when it comes to acquiring new spells. Mixing in another class only slows it more, and you probably can't afford that, especially since you're the main arcane caster for your group. (Past 5th-6th level or so, a strong arcanist becomes more and more necessary to the party's success.)
As you say, it was decent in 3.0 because you only needed one Pal level for divine grace, but 3.5 pushed that back by a level. Now I can't think of any situations where SorX/Pal1 would be superior to SorX+1, even throwing PrCs into the mix.
If you didn't want to stick with spellcasting, the opposite combination would be rather nice. A PalX/Sor1 is very nearly as good a warrior as the single-class paladin, plus he has access to a few very useful spells (like shield and enlarge person) and can use arcane spell trigger items. That doesn't fit your concept, though.
As you say, it was decent in 3.0 because you only needed one Pal level for divine grace, but 3.5 pushed that back by a level. Now I can't think of any situations where SorX/Pal1 would be superior to SorX+1, even throwing PrCs into the mix.
If you didn't want to stick with spellcasting, the opposite combination would be rather nice. A PalX/Sor1 is very nearly as good a warrior as the single-class paladin, plus he has access to a few very useful spells (like shield and enlarge person) and can use arcane spell trigger items. That doesn't fit your concept, though.