I get kind of irritated when people say stuff like "its still fine at the club level"--I am talking about any old car not just the T3. I don't know where you guys race but at our track we have some seriously good racers who could run with success at any track in the country (not including myself!!),
How many national a-main finalists? That will say a lot about how competitive they really are. If your running club races full of guys who make the show nationally we're talking about something entirely different here.
Yeah..T4 is a better platform than the T3, without a doubt, but if your not in it to win it there is no reason to force the upgrade. Want to have fun, want to just go race? Perfect. Want to win every race or take it to national race? Upgrade to the best machine possible, it can only increase your chances of winning.
Regular shmoe who doesn't care if he gets 1st or 8th ....it's fine. Otherwise he wouldn't be asking. If you really care about winning the question doesn't need to be asked in a online forum because you've already got top of the line everything.
Run it....if it's junk, replace it.