Dragons' Magic Items

[Chrono22]

Most dragons are intelligent, bordering or even exceeding genius. They know that having magic items can assist them in combat and to defend their lairs. At a certain age category, a powerful dragon is expected to have some magic items to augment their natural abilities.
How much of their hoard would a dragon be willing to devote to magic items? What proportion of a dragon's wealth should I, as the DM, alot to magic items?
Do the magic items I grant a dragon adjust his CR? If so, how much?

[Toliudar]

To the extent that CR is accurate, it's calibrated without factoring magic items (with the exception of humanoids, I guess). If you're going to dedicate half of a dragon's wealth to a bunch of magic items, it'll definitely perform above CR (I'd argue that dragons are usually more challenging than their CR indicates anyway).

[The Corinthian]

I generally assume that the dragon's relationship to its hoard isn't like a bank account, but more like an art collection. That is, the dragon doesn't think of it as wealth or a resource, and isn't inclined to spend it. Even if it would be useful, the hoarding instinct creates a blind spot in their thinking. There are some exceptions, dragons with little or no hoarding instinct or other obsessions which take precedence, but in general, I roll up (or assign) the treasure, then I see whether I got any items that are usable by a dragon. (Like amulets, rings or rods.) Those, it will most likely use.

[Runestar]

Wotc has not shown itself consistent in enforcing this rule though. The various dragons in red hand of doom each have a magic item, though one can argue that it alone is not sufficient to increase their cr.

[hamishspence]

Going by Dungeon magazine, a full array of magic items, including at least one major artifact, only increases an NPC's challenge rating by +2. (Warduke was the example I was thinking of).

I'd be surprised if dragons were any different.

[Devils_Advocate]

Dragons think of their hoards primarily as wealth, rather than tools. According to the Draconomicon, when calculating the values of their hoards, dragons consider magic items to be worth the half of their listed prices that they can be conveniently sold for. The upshot of this is that dragons will tend not to buy nor sell magic items. They'll keep and if possible use whatever magic items they acquire, of course. And they do have three times the standard number of random magic items for monsters of their respective CRs.

Going by Dungeon magazine, a full array of magic items, including at least one major artifact, only increases an NPC's challenge rating by +2.

What constitutes a "full array"?