For me it boils down to preferred signature and type of music. The HD25's to me are great with rock, quite punchy and fun, with sparkly treble and fairly impressive, punchy bass for on ear cans. The DT1350's offer more detail, nice treble extension but a bit less sparkle, and nice tight accurate bass, but without the punch of the HD25's, and rich, full mids. My listening leans more to acoustic, vocals, jazz and classical, then prog rock and 70/s through 90's rock. The DT 1350's are more my style (save for the rock, but decent with that), and I sold my HD25's to someone who loves that sound, and was underwhelmed with my 1350's.
Isolation is a draw to me, or a lean to the HD25, contrary to other opinions I've heard. Comfort leans to the HD25, if one can call either comfortable. Cool factor to the DT's, incognito to the HD's. Bullet proof and rebuildable to the HD25's, durability is likely a draw, the DT1350's really feel solid, well built and high quality. The cable is not as bad as everyone seems to think. Portability and packability to the DT1350's and their cool little case.
So, worth an extra $100? to me, sure. Headphones are my luxury, and $100 in that price range isn't too extravagant. If I was more of a rocker (as I used to be!) I'd go for the HD25's and be happier regardless of price.
Last, HD25's are more fatiguing to me.