First car, first Celica. Options

[Chreeis]

A bit of an introduction.
Growing up in NYC, we didnt have a car, because we didnt really need one. I've always had a strong appreciation for cars, and 4 months ago I got my first. Its a Red 1998 Celica GT hatch.

The bad:
She came with 2 pretty worn motor mounts, a trunk that wouldnt open, an intake hose held together with tape, as well as several other minor problems. It has ~235k miles on it. Last oil change was done yearly(if that).

The good:
Pretty much everything else. Just had timing belt and a few other parts changed <10k miles ago. Drives like a champ, no rough idle, starts right up even in sub zero temps. Trans fluid ok. As for the high miles, I am 3rd owner, and have been dating the 2nd owner since she got it fron her uncle, the first owner. Needless to say, I have a good knowledge of the history of the car. Majority of the miles came from first owner (who maintained it well), an older gent who was dating a girl in Jersey while living in Connecticut, so mostly highway

I love the car. Since I've gotten it, Ive fixed the trunk, done brakes and an oil change, swapped broken intake with SRI, and currently have the motor mounts on their way. Still have a couple very minor things to fix, but nothing else major. My only worry is the mileage. I would love to do some real performance mods, but the car is old, and I'm slightly worried that things might go south if I push her too hard. I guess I'm wondering what the community thinks would be the best direction to go with her. Do I take the old lady and give her the time of her life at risk of her health, or do I just focus on keeping her alive?
Also, been lurking these forums since before I got the car. Both the information here and the community involved are incredible, so thanks for that