what are some practical ways to gain HP by modifying am IS350

That is an oxymoron. No one tries to gain horsepower for practical reasons. And thus, there are no practical ways to gain horsepower.

Otherwise, it is a $30,000 car, from what I've seen. Practical, would have been a $10,000 car.

So: Sell it.

Get a cheap Mustang 5.0 for under $1,000, and put the rest into the engine. Then you will have a fast car, worthy of a decent amount of respect. Unlike your current ''luxury'' sedan.