Whether a racing wheel/rig setup is a worthwhile investment depends on how much you're into the racing genre. Beyond Grand Turismo 7, do you see yourself buying and playing several more racing games throughout the PS5's life cycle? Are you into other racing franchises like F1, Need For Speed, Project Cars, GRID, DIRT (Rally), WRC and Asseto Corsa? What's the likelihood the wheel/rig will become a white elephant taking up space after you're done with Grand Turismo 7?
I previously owned the Microsoft XBOX 360 Wireless Wheel and for me it was a worthwhile investment because from 2009 (when I bought it for $179) until 2014 (when I moved on to PS4), I used it extensively to play over 15 racing games. Beyond the immersion factor, the biggest plus for me was better reflex coordination compared to using a controller. With a wheel, I can dedicate my hands for steering movement, fingers for gear shifting (I prefer using paddle shifters behind the wheel versus a gear stick) and feet for acceleration/braking. My reaction time to navigate sudden tight corners and bends, brake and change gears instinctively improved versus using a controller when I had do everything - steer, accelerate, brake, change gears - with only my fingers. A wheel also has greater steering range to control how much to steer compared to a controller analog sticks.
Your decision whether to take the plunge or not is a personal choice while considering expected extent of usage and budget. I have no opinions about either the Logitech G29 or Thrustmaster T300RS. You should test drive both wheels at a demo showroom/game shop to get a feel of the pedals' movement and resistance, degrees of steering rotation, and the wheels' force feedback level.
Finally, beyond Grand Turismo 7, I would like to recommend you another racing game below. While it isn't a realistic driving simulator like GT7, this game will hook you in with its intensity, grittiness, aggressive AI (at higher difficulty levels) and sheer fun!
Good luck & enjoy racing!
