Generally, cars like that are stolen as they are quick cars and are easy to use for crimes like burglary and armed robbery. Cars being shipped off to the continent are usually far more expensive (no offence to the guy who has had it stolen) usually in excess of £35k. Old Subaru Imprezas are commonly stolen as they go like the clappers, are easy to steal and easily dumped when needed. Same thing with cars like this. You can get a full "team" of burglars in that car rather than stealing a coupé like a Z4.
Tracker in my opinion are hit and miss. I don't know about other forces, but in London, cars are fitted with Tracker receivers which can pick up a signal and it works great. Tracker can boost it if needed. The problem is, thieves are wise of Tracker now, which is why stolen cars are regularly dumped in quiet residential streets or industrial estates, so if they do have Tracker installed, they are generally found in a few days, if they aren't, they go pick them up again.
Depending on how heavily modified the car was, it may strip down well for parts so the owner should keep an eye on eBay/Gumtree (which is the worst for stolen goods) and for those selling it with little feedback or vague return address when asked.
It's sad thing and I hate how people so freely take others property because they are too thick to get a job and buy things of their own.