I'm interested in adding some power to my 8, but everyone says it's a waste of money because you can't do all that much to increase major horsepower without spending thousands and thousands of dollars.
How much power increase will I get with just an exhaust system and intake? Thanks.

Depending of how wise you use your money and products you purchase or invest on. A typical average catback exhaust and intake will minimally increase your horsepower to 5-10hp on an average. You have to get a dyno on proven products applied on our car.

everyone is right. Go to Racingbeat.com and read wht they say about trying to get power increases without FI.

I'm interested in adding some power to my 8, but everyone says it's a waste of money because you can't do all that much to increase major horsepower without spending thousands and thousands of dollars.
How much power increase will I get with just an exhaust system and intake? Thanks.

If your lucky maybe 5-10 hp to the wheels with both bolt-ons. Catback exhausts are more of a bling look rather than performance for an Rx8, so if your in the market for an exhaust get one because you like how it looks and sounds.

How much would a High Flow Cat give? 1-5?

I believe a high flow cat will give about 5hp...

you'll get the best NA gains by going with a midpipe, lightweight flywheel, and ecu that will lean the open loop.

stuff like intake and catback mostly make noise or provide slightly cooler air to the engine, neither will give you gains to write home about.

nothin bolt on will give you huge power increases.... but in the bolt on category the midpipe will be your best bet for the most increase, but there are disputes to that item due to emissions and the CEL illuminating.... finally if you want maximum power, you have to go turbo kit or interceptor X which is also very good.... basically good luck with whatever you do