Does anyone know what the effective level adjustment would be for a full-blown NPC? That is, one that was made using the PC rules instead of the truncated version most NPCs get. I'm thinking maybe +2. They'd have fewer hit points, but would have a lot more powers to choose from, making them much more versatile.
This is a really problematic question. I like the idea and wouldn't mind using it for a major character, but it really runs contrary to the game's design.
Issue #1: Too many magic items. Put five level 30 PCs against one level 30 NPC-PC with the same amount of treasure, and the PCs will probably get a bigger haul than all ten level 30 treasure parcels.
Issue #2: As you said yourself, NPC-PC's wouldn't have enough hit points. The fight would be very quick.
Issue #3: Too easy to shut down. Without a general save bonus (except a +1 for a human), a single NPC-PC could be completely shut down for several rounds by the combined powers of five PCs.
I can't say what the ideal solution would be, but here's one possibility:
1. Construct the NPC-PC using the "truncated" rules for constructing NPCs.
2. Set his hit points to be the same as a solo of his level. You don't want him going down in the second round, before he has a chance to use at least most of his best powers.
3. Give him a solo's +5 save bonus. This will help him to avoid being shut down all the time by the orb wizard.
4. Expand his power list to be the same as a PC of his level.
5. Give him the trained skills and feats of a PC of his level.
6. Reduce his level bonus to equal his magic threshold. Since he has a full list of powers, feats, and skills, the level bonus only needs to account for the magic items we're not giving him.
7. Give him 1 action point. If he's like a PC, he could gain more with milestones, but he can't use more than 1 per encounter.
8. Give him one or two magic items and some monetary treasure, all drawn from the party's treasure parcels for their current level. This is a major villain, so the party that defeats him deserves major treasure. (As usual, subtract the magic threshold from any enhancement bonus before applying it.)
9. Mark him as a Solo. I think that's about the power level he'll have if he's constructed in this way. He's got the durability of a solo, the treasure of a major NPC, and the versatility of a PC.