The N/A XR6's fetch a reasonable price in the private market as demand is strong. Alot easier and much better option to sell the car and upgrade to the T.
If this is not an option visit Mr Herrod for a chip, exhaust and intake as that really livens them up. Around 220 kw is not out of the question and would cost less to achieve than the cost to upgrade to the Turbo. It may not be as fast, but it would be comparable to the 220 V8 in terms of out right speed, maybe even faster
Sounds like you really need to decide if you are willing to try and enjoy your car for what it is or alternately release your frustrations and bite the bullet on the upgrade to the XR6T.
Cheers,
Colville