We use a knackered mk3 fiesta van at work for lugging filthy stuff about (same engine but non-turbo) and a recent oil, oil filter, fuel filter and air filter change has done it wonders, its now loads more responsive and my mate says fuel economys up on his recent longhaul trip with it. so yes, id say a service would help usually so youre prob looking at something a bit more serious, dead turbo?