This WotC article defines the Big Six as thus:
- Magic weapon
- Magic armor & shield
- Ring of protection (or a +deflection AC item)
- Cloak of resistance (or a +resistance saves item)
- Amulet of natural armor (or a +natural AC item)
- Ability score boosters
For me, paying gold for these items is basically saying, "I want this effect so much that I'll spend permanent resources to keep these effects on all day." These effects can be gotten temporarily, to some degree via
greater magic weapon,
magic vestment,
shield of faith,
superior resistance,
barkskin, and the animal buffs. Thus, it's a matter of spell slots for temporary buffs (even if they're Persisted, they can still probably be dispelled) or money (or otherwise acquiring these items) for permanent use.
In short, to me, the Big Six are OK because they're circumventable via spells. (Just make weapon enhancements cost half so they're the same as armor enhancements- +1 costs 1K, +2 costs 4K, +3 costs 9K...- and we're set.) If your group doesn't share these buffs (or something comparable or better, like
polymorph), you're in more trouble.
And if you aren't saving your money for these Big Six, then what are you spending your money on?