Impossible to say if it would help since it just depends on your environment. Let’s take the extreme case and imagine you had LEAD walls. Would a better antenna help? Probably not, simply because the environment is not conducive to wireless in the first place. But if it did help, then obviously you’d want to replace all the antennas (using only one would work, but the effectiveness of MIMO would be diminished).
This is another example of why I continually recommend not using PCI/USB wireless adapters, but wireless ethernet bridges. Such bridges give you far more flexibility when it comes to placement and orientation. And to make matters worse, a PCI adapter is often obstructed by the PC itself!
http://www.tomshardware.com/forum/41136-43-good-desktop...
What you might want to consider is perhaps using a well-placed repeater, perhaps somewhere still in the line of sight of your PC but with less obstructions between the repeater and the primary router. IOW, like the wireless ethernet bridge, a repeater gives you more flexibility so you can find the optimal location to bounce your wireless signals.
If wireless proves simply too tough, then you might be better off using powerline adapters, esp. the latest generation of 500Mbps and 1000Mbps models. They’re very good and eliminate the wireless issue completely.