Steve. Coilovers are a bit OTT for normal driving and I'd avoid them unless you wanted to so some track work. Also, they are not cost effective; a set would be about £600 or so, before fitting. If you wanted the car lowered, then a cheaper option would be to fit lowering springs - these would still provide improved handling and are used with existing struts.
The reason that your tyres are wearing in the inside like that, is down to the geometry settings (I think). When the Impreza comes out of the factory it is set up to understeer as this is easy for the driver to correct simply by lifting off. However, a favourite mod among drivers is to change this. In effect the tops of the wheels are tilted in so that more of the inside of the tyre is in contact with the road. This greatly improves the understeer and allows for faster cornering, however, the drawback is inner tread wear. It might be a suggestion to switch the rear wheels with the fronts.
As for the struts, I have 4 standard ones here so you can have your pick of them. My car is an MY06 WRX so be sure to find out if they'd fit.
Hope that helps