I'm not a suspension expert but I thought the GTV had independent MacPherson strut suspension (see http://www.motioncars.com/carchart/h..._romeo_gtv.htm
The benefits of strut braces on MacPherson strut suspension (wikipedia):
"With a MacPherson strut suspension system where the spring and shock absorber are combined in the one suspension unit, the entire vertical suspension load is transmitted to the top of the vehicle's strut tower, unlike a double wishbone suspension where the spring and shock absorber may share the load separately. In general terms, a strut tower in a monocoque chassis is a reinforced portion of the inner wheel well and is not necessarily directly connected to the main chassis rails. For this reason there is inherent flex within the strut towers relative to the chassis rails.
A strut bar is designed to reduce this strut tower flex by tying two parallel strut towers together. This transmits the load of each strut tower during cornering via tension and compression of the strut bar which shares the load between both towers and reduces chassis flex.
A direct result of this is improved chassis rigidity (similar to that gained from a lower tie bar); hence, the understeer is reduced, tire wear improved and metal fatigue is greatly reduced in the strut tower area."
To what degree does a strut brace improve the chassis rigidity on the GTV is up for debate of course. In reality the only way to assess this would be to fit one and see. From reading peoples experiences on various it seems to vary (no affect to much better handling) so how hard you drive the car will also be a factor.
I've got one on order so I'll let you know when it is fitted.
With regard to understeer some interesting info here.. http://en.wikipedia.org/wiki/Understeer
So 147 not so bad... 159 not so good. Whilst there may be no direct correlation the 350z has a strut brace fitted as standard and also has the lowest understeer rating. But then the Mustang has a low understeer rating and TG slate Mustangs for not being able to go round corners so who knows