In principle strut bars are very welcome and will not harm. It improves chasis stiffness therefore reducing flex. If you can get front and rear stut bars, even better. That's one of my next projects together with thicker stabilizers.
Strut bars are a great thing if you are using them as part of a package. Unless you are upgrading your whole suspension, I wouldn't bother. If you are going to add adjustable coil over shocks, bigger sway bars, different wheels and tires in an effort to make the car faster through the corners on the track then go for it! The IS-F is set up to work well as is. If you stiffen up the front of the car too much you will force the already too skinny tires up front to do even more work. You'll want to leave a little compliance in the suspension to help the OE front tires grip.
Shock/strut tower braces add to the rigidity to any chassis. Tom's offers a bar for the IS F exclusively as well as a full under chassis brace kit. VIP Auto Salon carries this for the F and is being installed on their project car. Check it here.
Jack, I almost purchased the TOMs upper mount sway but decided against it. It was fairly expensive and I decided that since I don't track the F often there is no reason to make the chassis stiffer. I just spent the money on other parts for the F
Flipside, what would be the advantage of the under chassis brace kit, just more stiffness?
Yes, I agree....if not tracking the car it will pretty much just be for show because you will not realize the benefits on the street. They are effective and if your trying to tighten your chassis as much as possible go for it!