The rewording and proviso added for 'The only thing you've managed to break so far' is still pointless dude. Retain Essence, as written in the Eberron campaign setting, gives you the full XP (direct to craft reserve) used in crafting the item you've broken down. All you need is the appropriate item creation feat for whatever you're dismantling and a day (8 hours) with the item.
So, as it is now, you're removing half the XP you could already gain to your reserve, for the sake of getting half the materials (i.e. gp) back too. This is what's known as a s****y deal where I come from. Cash is rarely ever a problem by the time you hit level 5 (where you gain Retain Essence as an artificer), but XP is at a premium for crafting purposes (beyond cheap potions and scrolls) until level 9 or 10 really.
You also need to elaborate GREATLY on the familiar/homunculus thing, since familiars have virtual HD equal to their master's, with precisely half the hp of your own and can run off your base saves and skill ranks if better than their own, whereas homunculii can have up to a maximum of 2 less HD than their master calculated like normal hp, and can only use their own saves and skill ranks. Both of these effects run off character level, not class level. Also, you should clarify whether this PrC stacks seperately for familiar abilities, or whether you add wizard (or whichever familiar granting class you have), this PrC AND artificer to determine familiar abilities, since your homunculus doesn't care how many artificer levels you have, just your character level.