I'm not really qualified to say much on handling specifics, although I do wonder how many miles your car has done, and whether you have some suspension components that need replacing ? I imagine that some of the more expert members here will be able to give you some more specific advice.
As for WIM, it definitely makes a big difference. I took my IS down a local road of "twisties" soon after having it WIM'd and I was amazed at the transformation. The WIM settings are available (either on this website or via Tony) and you could get someone local to set up the geometry, as long as those local people are competent enough to set it to those WIM parameters (e.g there seem to have been cases before where some garages don't really understand it).
Perhaps someone on the forum might be able to recommend a decent place to get this done near to you ?
I have a local garage close to me which have all the laser alignment tools they hook over your wheels for toe, caster, camber etc. The car is X reg 2000 and has done 84k and about 6 months ago had some springs put on - the car was re-aligned after the springs were fitted but not to Tony's spec. Do you know where i can find the Geo details at all...?
Cheers.