There's definitely much more noise in my car now. It was lough enough before getting rid of the seats, which also apparently acted as sound dampeners. It definitely doesn't help that my exhaust is pieced together by Autozone clamps and pipe segments, or that there's a visible hole near my rear passenger side wheel well from the rust. But, I only have front speakers in my car, so with the volume turned up a little bit, I can ignore the noise.
And, I didn't cover up the gas tank access stuff. It's just sitting there. I haven't smelled anything yet, so I hope it's good.
100 lbs out of 2000 may only be like 10 lbs out of 200, but it's still 5% of the weight. And, most of the weight I removed was in the back of the car, so I suspect that the placement had more to do with the handling than just the weight of it.
The back seats (seat and seat back) only weigh like 20lbs, but I really had a ton of junk back there that I kept thinking was better suited for the car than the apartment...but I was definitely wrong.
There's another Tercel driver who is meticulous about weight savings, and has posted his results
here. It's definitely a good baseline for seeing how much different things weigh, a few of them are surprising.