e: Reposting this lower down because I probably spent too long editing it. I'm interested to hear Han's thoughts on it, because it seems like a better way to houserule crits and sneak attacks for splash weapons, both in terms of meshing with the character and making sense.
If I were DM, I would figure out some way for crits and sneak attacks on the stuff with saving throws to increase the DC. I can see that (a good throw gets more of the stuff in the body), but massively increasing duration on a sneak attack makes...less sense.
The only questions are what bonus for a crit (+10?) and what for sneak attacks (+2/d6?)
2. I would actually love to see crits and sneak attacks increase DCs rather than add to effects. That would be brilliant, and would let those items stay effective into much higher levels than normal. Hm, a flat rate might not be the best for crits, considering that it would be far too much for lower-level items and too little for high-tier items. Multiply the DC by x1.3 on a crit, rounding up to the nearest whole number, perhaps? So a DC12 item that critted would have a DC of 18 for that attack, a DC25 item would have a DC of 37 for that attack, and so forth? That would come close to replicating the effect of a damage multiplier in terms of the effectiveness of the attack, keeping in mind that they'll only crit on natural 20s (unless I spend a feat just to expand my threat range with them to 19-20, which seems... wasteful).
For sneak attacks the dice roll for added DC seems good, assuming it scales with level. Maybe make it half the dice of my current sneak attack, rounding up. So for now I'd get 2d6 to DC, which would remain the same at 7th level, go up to 3d6 at 9th level, and so forth? At 20th level that'd give 5d6 additional DC on a successful sneak attack, which could range from near-pointless to a near-doubling of DC, depending on the roll and item. Just a thought.