Here's my 2 and half cents worth.
I was in the exact same situation as you two months ago.
Was looking at putting in the BMW PI, but then started reading compares between BMW PIs and the Euro Air Intake - apparently they are similar (using the cone filter instead of the drop-in), with the exception that the BMW PI sucks air in through a small section close to the windshield area I think. I haven't really checked, but I'm guessing our AU versions have Euro intakes (I haven't opened up the air box to check - someone here can confirm). I think the power gain claim of 3hp may not be night and day difference, just that your engine breathes better with more cold air; however, folks on the other side of the pond claim that the BMW PI and Performance Exhaust combo does give power gains.
With the front strut brace, I was thinking of the Alu strut brace as the CF strut is really just bling factor (both materials are light so weight diff is negligible). I researched a bit more and it appears that the M3 strut brace (to replace the current OEM strut) is better value for performance as they cost around $3XX shipped.
Fast forward to now, I've decided on neither at the moment and looking at the BMW PE instead. Issues with the PE is that it's not ADR compliant, so you run a remote chance (or just pure bad luck) of getting your car defected IF caught. So, it's a risk vs reward situation. But seriously, that PE sure gives your N52 a more meaner growl than the silent fart wheezes with the OEM exhaust.