Penetration is for penetrating magic resistance. It isn't about penetrating wards.
Would the penetration of a Pillum of fire matter when blasting a summoned wall of wood? that's the same situation spell interacting with spell. there's no resistance in the equation to penetrate.
It is worth noting that few, if any magi would use such a ward - bloody annoying when your silver goes flying away from you... (ward against any and all metal, remember) - not to mention that having raw vis in the form of rings, etc usually means magi likes to open for some metal getting near them. So usually, you'd find a ward against non-magical steel/iron and the like... (magical steel/iron can be warded against with the parma - it is nice to be able to wear that ring of vis on your finger...)
At a higher level (for selectivity) it could be defined as being against iron, but still.
Many SG's and Players forget details like that, or just don't think to look for them - there are many "side effects" of some certain spells that can be quite awkward.
why should it need to be of a higher level?
The standard version of ward against wood doesn't affect magical wood (probably due to a magus carrying a staff...), and it definatly doesn't affect all other vegitable material...
Because, imo, wood and "vegetable material" are as different as metal and stone. Ward against wood would not stop a tomato, but it would stop balsa as well as ebony.
The guideline reads:Level 5: Ward a target against dirt.That, for this effect, gets bumped up by 2 mags to "against metal", and we have our basic ward. "Metal" is all metal - not just iron, not just steel, not just steel and iron and any bronze in the shape of a weapon - "metal". Lead, gold, pewter tableware and the brass buttons on your vest and that ring in your ear - away.
By countless examples in canon, when a spell gets "tricky" it adds a magnitude (or more) "for complexity".
That's why.
(And I'm not sure where you're getting that bit about Ward Against Wood - in the core book it's all wood, no "magical wood" exceptions.)
It is there. I got fooled by that as well. It is in the description of one of the spells, but not the guidelines.
The guideline itself reads: "Ward someone against mundane plant products."
The spell "Ward Against Wood" expands on that guideline (IE: Makes its ineffectiveness against enchanted wood explicit and inarguable), but the guideline itself is there.
For my part, I've always ruled that "Ward Against X" spells only work versus mundane examples, excepting the General guidelines, but it's certainly not clear.
Hmmm - "non-enchanted wood" - you're right! (Damn this headcold!)
That's interesting, because that completely undermines my position that an enchanted object is both magical and still a mundane representation of that Form.
Hmmmm.... I think I may be reversing my position on that one. But I'm not doing anything until my brain doesn't have to fight thru one Aquam amount of mucus.
Amp up your sugar intake and drink a lot of caffine and vitamin C.
May not be good for your diabetes or heart condition, but it gets you up and going 
(The thing is, I actually took the time to specifically re-read that very spell before posting the first response - the spell description is only like 5 lines long - and I completely missed the word "non-enchanted". Completely! Like it wasn't there.
This is a bad one.) 
Thus came a new market in tomato arrows... shame they're native to the Americas, we'll have to wait a couple centuries.
(Throws a tomato at Jachra, all the way from the americas)
Use Turnips or radishes. They are just as effective. Come to think of it, a radish might make a good arrow head.
Cowpies are effective too.
Are we in agreement though that the penetration of the sword itself is non-interactive with the ward?
Seems so. It goes against my gut feeling, though....
Xavi
My one ex is from Poland, Kracow specifically. Told me all about the cool dragon that used to live there. But anyway, she insists that Poland has had tomatoes and potatoes all along. She simply cannot imagine these things not growing native in her home soil.
She's the kind of girl that you eventually get tired of telling her that she is wrong, and you just give up. Tried explaining that peanuts weren't really nuts once. Very frustrating.
LMAO 
Maybe she just needs to translate peanut and nut to Polish then: they are unlikely to be related in other languages than English
Cheers,
Xavi
LOL, I guess that the Polish word for Peanut translates as "ground nuts", as in nuts that come from the ground as opposed to trees. That just made the debate even more pointless.
And I have a child with this woman!
The boy is already proving to be more agressive and quick witted than she expected. She is actually pretty intelligent. It is just that the education she recieved in cold war Poland was somewhat lacking.
Curses! My wood-only Herbam ward is fruitless!
Is this why she's your ex? rimshot
Sorry, sorry. 
It always baffles me how some people can be so thoroughly blind about history; I met someone who thought the Americas had been colonized in the early middle ages! I asked him whether Charlemagne was involved and he just gave me a blank look.
, it is cool. It was a combination of factors. As I said, her disadvantage was a lackluster education system as she was growing up. Cold war Poland was a pretty messed up place. She is actually very smart when it comes to pragmatic matters, such as finances and life management skills.
The tangential point is that ignorace of history is not limited to just Americans 