Welcome! Sounds like you’ve got some good Bolt-on’s, there, is the Car running strong with no CPU Codes- pass a State Inspection? Unsure of where you are- but Vehicle Inspections are/are going to be becoming more brutal every year- just need to keep that in mind when pointing at more power. A set of good Long Tubes would be a worthwhile mod- no matter what direction you eventually do go, your exhaust system will need to be able to breathe- I’d bet Headers will allow you really gain a good bit from your current setup. Exhaust System already a good, Stainless High CFM X-pipe setup? I’d mentioned Stainless primarily for longevity..
You’re going to get to the point soon where, if you seek more HP- you decide if forced induction is for you, or you want to squeeze all you can out of it normally aspirated. Pro’s and Con’s in both. You could also get a wet NOS kit, hardline type, TB plate and grab 75-125HP there, safely- in 1 or 2 Stages. (Get your Tuner on board if you do, to ensure your Motors Tune(s) are updated for its use, and also yield all of its benefits). Unless your reciprocating assembly is better than stock- wouldn’t go too far above that, never above 50% of your Motor’s Stock Crank HP is a relatively good rule of thumb...
Does the Car Plant well- use what HP it now has effectively? If not- improve on that end. Good Tires, Brake upgrades,
Suspension -all need be matched up well. Keeping it all in balance is really the key to having something truly formidable- predictable- and safe.
Took me a couple grand and my labor to hook up and correct handling, lighten and improve the lead front end bias in my GT500 when it was still Stock- otherwise, it was really only an overpriced burnout machine. All the HP in the world won’t help you if you can’t plant it, or use it in the twisties, or Slow down hard multiple times without your Brakes fading out in a 30 Minute- all out full bore ‘fun run’, beginning to end...
So- if it is a true power boost you want- Headers are you’re best investment- you can’t lose, eventually you will need to get rid of the restrictions your Manifolds impose. NOS is a good leap and give you insight into how your Car will handle another 100+ HP or more- when it’s built to that output, eventually. Tweaking your Tune(s) is also another good Avenue, be sure to ensure from your Tuner what you have is safe for using your NOS to keep your timing from going overboard and detonating- as I’m sure what Tune(s) you have is already pushing Timing Advance to the edge... Your Tuner should be aware of, and will likely modify for every HP increasing Bolt-on, including Headers.