Pgarner is correct, diesel engines are generally heavier than similar sized petrols so the 1.9 unit in yours will be quite weighty. That can't be changed. As previously said, there's not a lot you can do with a NATASP IDI diesel really.
You can use cetane boosting additives. Millers Diesel Power Plus or its later replacement Millers Diesel Sport 4 will help. As will high cetane fuel, Shell V-power, BP Ultimate and Total Excellium will give a little more torque, which will make a difference to pedal response. These all will help to remove injector gunge - that too will help over a few hundred miles.
We have a Seat Ibiza here with the VW 1.9D engine and it, although slow with its 73bhp output, does feel quite pleasant now it's clean and running properly. In some ways it's nice that there is NO TURBO LAG or TURBO spool up to wait for at all. It's no match for my mapped 406 (192bhp and silly over 300lbft torque) but it's easy and lively in its own way. And it will stand up to 8mph in 3rd gear and take off again quite happily.
Clean air filter will help, as will clean fuel filter.
If you want to be brutal, then use an oil flush additive when the oil's changed. Fill with a decent synthetic of the recommended viscosity.
Check for lost motion on the accelerator cable at the pump end. Slack accelerator cables can make cars feel tardy and lifeless.
Before you make massive changes to the suspension, how about getting all the bushes replaced? And fit some decent tyres if the ones one there are questionable. Get a full four wheel alignment.
Now see if you still want to blow hundreds of pounds on 'stuff'.