I think my 2 gutter runners have more SPP's than anyone else in the whole league.... no-one's managed to kill them yet :p It's out of fear of that happening that I bought a third. I think I used at least 1 SPP on making one of them harder to kill. I've seen games where people focus too much on my gutter runners, letting my rat ogre & friends bash it through the middle

With 4 gutter runners on the pitch, no such plan B exists.
Re: Stormvermin (Blitzer). I have one but he doesn't do much. At all. Still not entirely convinced they are worth the extra 40k.
On the subject of the thrower I still don't think I'd bother long term. With a starting team Sure Hands is invaluable (just ask a Chaos coach) but AG4 is almost as good (Percentage wise you're looking at 16.67% chance of failure for AG4 vs 11.11% for Sure hands... I think, Help me Gandy!). Apart from that Pass has the same argument as Sure Hands and the extra ST shouldn't come into play unless something goes wrong.
My thrower (The Brain) usually sits back in a quarterback-style position. He is often called upon to stop offences - the extra ST really helps here, eg I get to roll 2 dice against a goblin, or roll 1 dice against a normal ST3 guy. Often a gutter runner or 2 gets back to help with the block too - ST doesn't matter for that of course.
I think your numbers are right, though all you have to do is get Accurate as a skill then throw like an AG4 character anyway. I haven't played for over a month. We really should start playing again...