Until now i haven´t seen a spell that causes more than one specific effect (exception from this are indirect combat spells with several elemental effects, but they don´t count because it is just more damage). But what about e.g. health spells that combine 2 effects like "increases strenghts AND increases agility"? Would that be too powerful?

Pump the drain and go with it, I says. Not so different from a combat spell that lights fires and shorts out electronics. I mean, it's a bigger effect than that, but it's a difference in scale, not kind.

Remember, you're balancing it against the fact that a person can cast the two individual spells at once. Make it a trade-off the caster would have to think about for a bit, and you've done it right.

You could always multi-cast.

EDIT: But then you're sustaining two spells, gotcha.

Such spells probably should not exist; sustaining penalties (and the costs for quickening, etc) wouldn't mean much if you could design a combined "boost all attributes / combat sense / invisibility / levitation / magic fingers / armor / death aura" spell. Drain alone isn't enough to limit the power of sustained spells, not when they can cast outside combat and use all kinds of med-tech and magical help to (just barely) survive the drain, and keep the spell running long term after that.
An obvious exception is illusion spells; they can be designed to affect only one sense, or multiple senses, but in that case they still really only "do one thing".
In game-world logic, consider how hard creating and casting a spell is supposed to be; spells require intensely focused will. How realistic is it to focus your will single mindedly on two divergent purposes as part of the same task? It would be like asking why there aren't cars that let you drive two directions at the same time...

So, short answer- yeah, I think it would be to powerful.

It's also only one spell you have to counter to bring it down.

Also, if you're adding little enough drain that it ever makes sense to have five or six combined in one and survive casting it, you're wrong.

I suppose in SR4 its different. In SR3, drain codes couldn't go over "D", so you'd have something like 3925(D) drain; obviously you'd fail any resistance roll, but so what? Its still just 10 boxes, which a simple trauma dmaper / platelet factory would let you stay conscious through. SR4 does fix that nicely by piling on more and more boxes, but it still strikes me as setting a bad precedent to allow a spell to do more than one thing, because as soon as folks find a way to get around the drain, you have a problem. Say they pump out a combat spell that launches both a mana ball and a fireball and a stunball and.... er, not even sure ho you would resist that.

Yes, in SR3, nukes can't kill people. Hilarity ensues.

Me, I'd say the additional effects should be like adding different elements to an elemental spell... The damage doesn't go up, just the side effects... So in the case of Increase Strength and Agility, for example, the hits are split between the two stats. *shrugs* That's my solution, anyway.

Rigger 3 (IIRthetitleC) introduced 'naval damage' for vehicular (or just plain BIG) weaponry, giving a further four damage codes continuing in the triangular number sequence:
L = 1 box = 0 + 1
M = 3 boxes = L + 2
S = 6 = M + 3
D = 10 = S + 4
LN = 15 = D + 5
MN = 21 = LN + 6
SN = 28 = MN + 7
DN = 36 = SN + 8

It was a great (IMO necessary) addition that meant there were weapons that could reliably kill trolls. I don't remember seeing a damage code for a nuclear weapon, but it would (should?) have been higher than D.

But then, if you're actually rolling dice to try to survive a nuclear explosion there's something seriously funky going on in your game!

And yet hundreds people survived Hiroshima and Nagasaki, some as close as 200 meters from the blast centre (under some cover, granted, but still)... humans are amazing at surviving against all odds. (Also, some Haitian can probably tell you about surviving for days under rubble that looks very very deadly at first glance)

Interesting, I had no idea. Well, you know what they say about learning a new thing every day.

Of course, the nuclear militaries of the modern world sport warheads far more powerful than those used in WWII, but smaller ones do still exist for the enterprising supervillain.