VoP improves your numbers. Magic items can do anything. Therefore, instead of being able to purchase anything, you just get better numbers. As a caster, you'll have to give up caster level increases, metamagic rods, etc. As a melee type, you'll have to give up true seeing, teleportation, flight and have to overcome all the hurdles melee types suffer of without access to the spells that normally overcome them. Oh, and you can't get any useful weapon special abilities.
Basically, while the numbers of VoP may look good (they are for the first 5 or so levels - indeed, a VoP "non-armor character" can easily break the game by simply having the equivalents of high-level Bracers of Armor that works with their unarmored style). Once you start to put together funds to buy more effective items though, VoP swiftly loses its luster as it never grants you all the good stuff (seriously, try to replicate Belt of Battle with the feat; hell, initiative-boosters are practically impossible to come by let alone inherent stat bonuses or the like).
As soon as you can afford few magic items, VoP starts to restrict you more than it helps you. Good luck fighting that Dragon without being able to fly. And your casting ability is severely hampered by lower caster level and not being able to spontaneously apply metamagic through Rods, not to mention stuff like Ring of Spell-Battle, Ring of Counterspells, etc. VoP replicates the basic number buffs but nothing beyond that while items generally do everything else too. VoP tries to replicate what your wealth would get you, but it's more restricted and doesn't give you the best, most important pieces because they're class-specific and VoP is general.
