Methos, the post on TWF is the most clear analogy I've seen.
Practiced Spellcaster REDUCES a penalty.
Spell Penetration gives a REAL BONUS.
a pure warrior bends all his feats to combat (for the sake of argument).
a pure caster bends all his feats to casting/crafting (again for the sake of argument)
a warrior/caster splits his feats, and now he has to consider giving up one of his
few feats just to have his LOWER LEVEL spells on par with the LOWER LEVEL spells
of the rest of the party.
Thanee nails it on the head in pointing out that having the highest level of spells
trumps any perceived advantage over a mutt caster having practiced spellcaster
feat.
TWF for warrior types, Practiced Spellcaster for caster mutts. Same thing.
You know, you could make a deal with the ArcTrick in your game and see if
the feat actually makes the character too powerful. If it doesn't, well, your
problem is solved and you can stop reading this thread
the ftr5/sor1 w/ practiced spellcaster? Ooh, so powerful. Maybe he just gets
a 1st level pearl of power, asks the 6th wizard to cast mage armor on him,
and he'll give the spell slot right back
1000gp, 6 hours mage armor, no feat wasted.
mage armor + shield + dex = nice AC at level 2, even 4.
At level 6 to 8 you can face stone giants with +18 to hit.
In fact, monster bonus to hit (including strength) tends to add up to +5 per
two PC levels, if not more.
at level 10, see if fire giants aren't +20 to hit with a greatsword.
Your problem is self-solving, and in fact the ftr5/sor1 has nerfed himself for high
level because he probably could do a lot better if he were a pure fighter wearing
chain shirt +4, which is +8 AC, all the time. (Ok, so it's not a force effect, and
incorporeals ignore it. Wah.)
Mage Armor and Shield? he'd get more mileage as:
Ftr4/bard2. wear light armor with no arcane failure. Be able to activate a wand of
cure light wounds (which all clerics make dozens of over their career

and have
some decent spell choices, plus contribute a bard song twice a day, freeing up the
cleric from casting bless and doing prayer instead before beginning the flame strikes
With one level of sorc, I'd be a fighter in full plate with these two spells:
True Strike
Feather Fall
both are verbal-only, suffer no arcane failure, and you can skip practiced spellcaster.
(True Strike = auto-disarm, auto-hit with a maxed power attack, etc.)
Sounds like you have a good gaming group, but they aren't even close to powergaming
3e/3.5, and they probably don't care to.
Practiced Spellcaster won't make your campaign world any worse. Multiclassed
casters were always too weak for the few spells they got. A straight fighter with
a good rack of potions or caster support behind him is much better than a caster
mutt, so let the mutts have their practiced spellcaster bone.