Base Boxster performance progression

[56 Spider]

My 2001 base Boxster performs well at DE events at Sebring but it's time for some more power. Safety first so I have upgraded with Porsche sports wheels, drilled discs, OMP seats, Schroth harnesses and Brey-Krause roll bar. I know I am not going to keep the Corvettes and 911s on the straights (maybe in my Ferrari 430 but I am not going to subject that to Sebring's bumps!), but some performance gain would be appreciated. What is a good path to more power?
Intake snorkel - most people say it is not worth the minor gain
Sports muffler - lots of complaints in the forum about droning at 3000 rpm, and this is a road car too so that won't work. Any good suggestions?
Re flash the ECU - which one is a good option?
Increased mass flow rate sensor - which one?
Any other good thoughts?

Thanks for any constructive replies!