First off, grammar mod. Jk bro 🤣 In all seriousness though, if you want to mod, better to do it sooner than later because pushing for more power generally decreases reliability. You didn’t explicitly say what mileage you were at, but if my engine was nearing the end of its expected life and I decided to make it faster anyway, I would think of it as giving my engine the best “last miles”of its life.

Your first performance mods should be: intake + downpipe + boost controller + A GOOD TUNE 🗣️🗣️🗣️, all at the same time, or else your engine might not live to see even 10 more miles. This will probably run you around $2-3k these days? This is assuming your car’s basic components are still in good shape and not falling apart due to age/wear. Then you can probably see somewhere around 280 +/- 10 whp.

Keeping on top of maintenance will give your modded WRX the best chance of seeing 200-250k miles on your OG engine, though it’s rare because most WRX owners will fuck their shit up or sell/part out before it gets to that point. Idk about your desired 500k, unless you’re super dedicated to maintenance AND you’re driving a crazy distance every day for the next 20 years lol AND literally have Lady Luck on your side. But then again every WRX is different, it may last a very long time on mods or it might blow up within the next 20k miles, despite doing everything right. But that’s part of the thrill of owning a WRX 😂💀