True...to a degree. Yes the W58 gearbox isn't as strong as the V160. The engines while there are differences are also both fairly strong. However going NA/T isn't cheap by any means (doing it properly that is) and high power figures have been attained.
Not a great deal for the amount of cash you will spend.
There are plenty of threads on weight shedding. Have a look.
I have an N/A manual as a daily driver, does fine even with the triple plate clutch and cusco diff, little hairy but all depends on the right foot. The auto is lovely as well, I had an NA auto and it is still a rapid car and is lovely on the motorway. As far as being sensible, probably not, there isn't much boot space and it can only REALLY carry 2 people in any comfort.