I definitely like the halving move speed, that's an excellent idea. Can't run either.

I dunno still, I think the point of those stances is just that they are just better than the average adventurer (aka, not PrCs) with a sword, so they can focus a little more on defense or offense without giving up the other. Thats why primary stance is just a small bonus to all. It's more like giving up the +1 AC from primary to get offensive bonuses.

If I did rework it to be plus and minus, I think I'd also increase the bonus very slightly. Although I am still a little worried about whether it is slightly overpowered, I'm not really sure.