I had the 1992 Astra 1.4 hi torq - it was a bit slow. HI Torq seemed to mean low speed. It also didn't have power steering. Have you thought about a sports exhaust? A friend of mine fabricated one for me with a large center silencer and no rear silencer. This actually helped kick up the power a bit and it sounded great. I think he used a cavalier extension box.
As Xedan suggests a panel air filter will be a good cheap mod. (Get a high flow sports filter though)