You`re thoughts for buying items are solid, in AP/CW even better since there upgrading neatness skill gives you crystals and runes destroying items , highly needed later in game.
As you play original the Legend divorce takes 20% which can be allot late game, but depends how often you change wives (if you screw around, you should lose all you`re gold
). But For huge amounts of gold you gather during game, best solution is buying runes at Tibold dwarf prince because only other choice is buy units/items. Here you cant buy leadership, experiance, permanent bonus to stats, or rage/mana. All other things in game are for limited time usage , so hoarding gold is useless.