Yes, as long as it has a full service history, or has been owned by an enthusiast, or you intend to drop the sump, get it cleaned and take the rocker cover off and clean in there too.
The 2.3 engine needs fully synthetic oil as it runs hot. Semi synthetic breaks down too easily, causing sludging. I always changed my oil every 5000 miles. 5 litres of synthetic is under £25, and a filter is less than a tenner. It’s an easy job.
Joolsburger is partly right – the oil breather is the problem rather than the sump itself, but with a 2004 it should have the revised breather already fitted. The sludging of the sump actually ends up blocking the pickup tube and starves the top of the engine (and turbo) of oil, eventually killing it.
A sump drop and clean is under £200 at a garage that knows what it’s doing. Not worth doing yourself (IMO) as it’s a pain to get at all the bolts.
Rear tyres worn in “steps” points to the bushes.
Um, what else… They’re a heavy car so do wear suspension parts, but front bushes are not too expensive. Check that there’s no excessive rattle from the chain. Check that it’s not hard to start from cold, and that there’s not lots of smoke from cold (often valve stem seals). As it’s the Aero, give it a razz in 3rd, 4th and 5th, and check on lifting off that there’s no smoke (worn turbo, and a few hours to fit a replacement, excl. parts costs). Anything else is just usual checks on a 13 year old car – check the gadgets work, bodywork for rust, usual stuff.
I disagree that parts are expensive. Some engine parts are, but wear items are not, especially compared to BMW, Merc and Audi.
They’re a reliable and long-living car if looked after (isn’t everything?) and the only real quirk is keeping the engine fed with synthetic oil every 3-6000 miles.
I’ve had 3 Saabs (2 9-5 Aeros) and would have kept my last one had my circumstances not changed. Email me if you fancy a chat.