Well, people have mentioned making the magic items necessary... what about wanted? People will naturally want to get their hands on the artifacts. For heavily twisted fun, go watch the Jackie Chan Adventures toon. If the artifacts are easily transferred, you can easily set up a quick-change battle with artifacts changing hands, foes with spiked chains grabbing items from the rafters, and all manner of cunning plans.
Any plans to use the Eye and Hand of Vecna? Or disguise them? Perhaps change them to a jewel with a dark flaw at its heart, and a gauntlet with no opening to put your hand in; the opening is covered with a flap of leather. Only when you 'install' them do they revert to their true form.
Who made the artifacts? And do they want them back? Are they part of an ancient deity that was split up and wants to be reassembled? If so, how does it trick the PCs into taking it to the Place of Assembly?
Who else has artifacts, or knows where they're hidden? If the PCs become used to having these powers, what happens when they go up against similar beings?
Above all else, planning is important. Bad guys have to have massive scrying/spying resources to lay their plans, and don't forget to make them watertight. Things have a bad habit of going pearshaped anyway. But a massive plan of attack, involving kidnapped bait, traitors amongst the PCs (who will likely not be traitors after all), and bizarre monsters in death-trap environments can always be fun. Really, I think Jackie Chan Adventures should be a must-see for someone planning to run this scenario.