To me WTAC it is not about running at SMSP GP, but more about showing off what you have done to the car and the sponsors all over it. So a public display which you won't get at any other Amateur event.
I myself am not interested in such an event, I only live a 10-15 minute drive from the track and have never actually been to WTAC.
You are better off doing a NSW State Supersprint run slowly by ARDC to get laps in. That is pretty bad for the non NSW people out there.
At the final round the day after WTAC I completed all 4 sessions(that is very low should be at least 5!) which was 23 timed laps in total which were all clear except for lap 1 where I had to push a Golf R out of my way.
BTW, that wing was probably slowing you down and likely making the car very light in the front for Turn 1. Needs some fencing and timber material installed up front as well.

I used to hit 190 to 195 down the straight in my previous SE which only had an Exhaust and Intercooler.
You will need a lot more power to go faster. My current 200kw ATW SE hits 215 to 220 depending on wind direction.