That is as good a reason as any, the Bridgestones are still good tires.
Given that this won't be a track car I'm sure the SPC stuff will work fine for you, but to add to your first question on what other FIGS bushings would benefit you -- consider the rest of the bushings for the front suspension (lower front, and upper control arm bushings). Those are all relatively big, squishy bushings and should help the precision of the steering and front suspension.
I don't have any personal experience with MOOG on my IS, but I know they make good parts, let us know what you think of them.
I don't have any experience with the various under-car braces that are available, but by opinion is that they should help more than strut tower braces. All the major suspension pickup points for the car are low under the car, these chassis aren't known for their stiffness, and from working under the car it seems like a no-brainer to me to tie together some of the hard points on the front of the car as well as the rear of the car.
I'm definately not the exhaust guru. My exhaust is stock, and if I change anything on it I will start with headers and go from there.

 

MOOG so I hear is the best brand but expensive. I ordered all four tie rods and both front lower ball joints. $400 before tax

 

Didn't FIGS have a kit that came with all this and more... maybe the same but more expensive?

 

^FIGS makes a scary serious "PROAngle" front suspension replacement for the IS300, which replaces all the suspension arms, ball joints, etc on the front end of an IS300 to make it better for drifting, but I don't know that they sell any OEM type replacements for tie rods or ball joints for the ISX50.