But Concentration IS a con-based skill, that's just how it is. You're not penalizing the player for not knowing the system unless you hide the fact that it's a con-based skill.
It's there so wizards don't just nuke everything they run into, and it forces you to choose between a high-Int build where you have more spells or one that sacrifices some other stat so your spells don't get interrupted. By making it Int-based you're buffing Int-based-casters and nerfing Wis/Cha-based casters. When it's con-based (as the description suggests it should be :P) then all three flavors of caster have equal access to it.
Diplomacy and Sense Motive are feeling lonely with no Paladins around ;)
For saving throws I meant better-out-of-two. It's a bit silly, really? Let's say you have a fireball that lets you save with Dex. So a rogue could nimbly save reliably, but a clumsy wizard can't dodge a fireball at all. (Which makes sense, no?) Now you're letting the wizard somehow ace the REFLEX saving throw with his Int, which doesn't make sense...
Aside from not making "lore/fluff" sense it means that wizards are now as good at dodging spells and traps as rogues. ???
The fortitude saving throw (Con, now Con/Str) also doesn't add anything. Fighters will take both Con and Str anyway, while casters and rogues are likely to take neither. So there's no benefit to any class by the change to con/str. Fluff-wise though you're making a saving throw vs poison or disease with your FORTITUDE, which is tied directly to your constitution (ie physical toughness, overall healthyness), not your magnificent muscley arms. Being able to crush a boulder with your bare hands won't help when you have the sniffles... I don't see it helping (buff/nerf) anyone by being con/str, unless people like to build all-str no-con fighters.
The Will saving throw (Wis, now Wis/Cha) is all about how well you can resist mental influences with your willpower (which is a product of Wis). So while weak-minded fighters and easily-distracted wizards might be fooled by illusions, the down-to-earth Rangers/Druids or divinely-aided Clerics might be able to see past the trick. Let's be honest, nobody takes Cha in DnD inspired videogames. Unless you're a bard/sorcerer/paladin. Of these only the paladin is likely to have some Wis (but he's not in Veins anyway) so you're really only helping Sorcerers. You could make an argument that Cha is somehow willpower related since it's about force of personality, but that's just arguing for two stats (wis/cha) to do the same thing, and that's silly.
Also saving throws don't exist in 4e anymore... no wait they're more like static defenses.... no wait. Argh! Uh, just be careful applying 4e design principles to earlier PnP mechanics, there's a reason it's a seperate edition and not an expansion to 3.5e haha. I like this "multiple ability dependency" you speak of. Fighters want con/str/dex, mages want their primary caster stat + dex/con, but nobody has enough stat points to go around and make their perfect build. So you have to spread yourself thin, especially if you're an advanced class like bard or paladin. That's always been part of the charm, for me. Compared to being 18/00str, 18con, 18dex half-orc/half-giant barbarian. ;)
MM is "remove hp directly". No saves, ever. That's what the spell is all about. You're sacrificing a first-level spell slot to put in a 1d6 ranged damage hp removal.
You could have taken sleep, or color spray, or mage armor or something utility, but you don't have any damage output as low level mage. So you take some magic missiles.
They might do 2 damage, and you cry. Or they do 5 damage and you're pretty dang happy. But you can cast 3 at most (so 6-15 damage, 10ish average) (in regular srd) which means you can kill ONE beefy fighter, if you're LUCKY.
Later on you get stuff like fireball and acid arrow, which lets opponents save, but that doesn't matter because those spells do a HECK of a lot more damage.
To be fair when you're going up against later enemies you'll be shooting your five high level slots worth of "miniature imploding sun" that the enemy might save for half damage against instead of your 40 first level slots worth of "magic missile 1d4+1 damage". Magic missile is a low-level stepping stone to better spells, no sense nerfing it.
(Mostly I'm just a stickler for MUH TRADITION)
Besides, nerfing MM indirectly nerfs Missile Storm (
http://www.dandwiki.com/wiki/Missile_Storm_%283.5e_Spell%29) or the equally fun NWN variant Isaac's Greater Missile Storm (
http://nwn.wikia.com/wiki/Isaac%27s_greater_missile_storm). :D
I never keep using MM, even if it gives additional missiles to higher level mages.
OH WELL, that's all just me complaining. I like complaining, don't take it as a personal attack. I'm sure there's plenty of changes to be made so you can make SRD work in a videogame, some of the changes just look odd to me. I'm mostly familiar with 2e and 3.5e so when I see people change the rules (even 4e) my reflex tends to be a melodramatic NOOOOOOOOOOOOOOOOO. Doesn't mean I won't play Veins in the end :B