OK - a few things here.
1 - In my experience, sorcerers very rarely take magical item creation feats, because they can usually make so few of them - they don't often have all the required spells, so their ability is very limited.
2 - Sorcerers can use magic items without the use magic item skill. They can automatically use any spell-completion or spell-trigger item (i.e. wands, staves, scrolls), so long as the spell it casts is on their class spell list - even if they can't cast it! And, of course, they can use any wondrous item, armor, or weapons for which they make the requirements.
3 - Sorcerer's Charisma DOES affect their spells - they get to cast more per day and the DC goes up for higher CHA, exactly as a wizard's INT. They do NOT, however, get to learn more spells then the table indicates, barring feats or house rules.
4 - Eschew materials is such a negligible feat anyway, in my campaign, sorcerers get it for free. No trade-off required.
Now, to answer your question...
Spellfire is not something I'm familiar with, so I can't really comment, but it seems like, were I playing a sorcerer, I would totally trade magic item creation ability for it, if it does anything cool at all. Something I wouldn't use for something I would? Sounds like a deal to me!
Would I allow this as a DM? Probably not. At least, not for free.