The suspension has probably been changed due to the sls units dying, so the original suspension is probably useless, however if you don't like the coil overs they are the same for the impreza so you could sell on for around 400 depending on which bc's they are, and get after market regular ones for cheaper than 1 sls unit from subaru ! you can tell by looking at other cars that have sls fitted they look like a dog scraping it's bum along the floor when they have gone.
Heads are dependant on how the cars been looked after, driving on boost when the cars cold will kill them pretty soon, however the pic you posted the chap has a classic in the background so I reckon he knows what he's doing with them.
Don't expect much change from a grand for the heads doing from a specialist double that at least from a subaru dealer [emoji33] it's easier as an engine out job but can be done with the engine in situ, don't be put off by this as there's loads out there that have seen over 100 on the original gaskets.
Parts and a skim of the heads aren't that expensive it's the labour that's a killer.
Wheel bearings tend to be a bit of a weak spot but you'll hear that on a test drive, also a slight clunking from the front end may occur, I've changed shocks,springs, top mounts, anti roll bar bushes and droplinks and it's still there !
If it doesn't sound to loud and nothing is falling apart I wouldn't worry too much.
If you plan on keeping the car for a long time a remap may be the way to go, outlay is again around 500 but mines already paying me back in fuel, I used to get around 75-100 miles out of 25 litres it's now up to about 150 miles,
Long trips are even better, saw just over 22miles out of 40 quids worth of petrol last week [emoji51] ah and i find the turbos only really run well on vpower
if it's an 05 tax should only be around 280 as opposed to the 55 rate of 500 [emoji26]
Suppose if it's worth it is up to you, how it drives what smiles it puts on your face and costings add up.