There is an argument (which I don't really believe myself) that a "commercial" license (i.e. CPL or ATPL) will be the only way to fly IFR in Europe one day, if the airline lobby get their often expressed wishes.
This would be a seriously dire scenario which would ground the vast majority of the existing private IR (both FAA and JAA licensed) pilots, and is one reason I did the FAA CPL/IR. However I don't believe EASA would allow it to happen, and it would breach ICAO anyway.
This however is the argument in favour of doing the CPL/IR exams, and doing the extra CPL flying which is about 10-20 extra hours and is 100% VFR stuff.
The JAA ATPL is unreachable for a private pilot because it needs multi crew cockpit time, but the exams are said to be nearly identical for the CPL and for the ATPL. Only the PPL/IR exam set has a slight "discount" off the ATPL set.
Neither the CPL nor the ATPL (whether FAA or JAA) has any meaningful legal value to a private pilot in Europe, because the privileges cannot be exercised unless employed by an organisation which has an AOC. It is possible for an individual (as the business owner) to get an AOC (typically for goods/mail transport) but I don't see many openings for that.