Looking at current summer seasonal fares, 90 day AP one-way Main fares look to be around $1100 from DTW to many EU destinations (K fares), while roundtrip 90 day AP, 7 day min stay Main fares look to start in $1400 range (mid-week travel V fares). If you paid something in that range for roundtrip, there might be some value if not used on an EU return flight, but not a whole lot.