I would say that it is worth it if you save up for it and happen to have the cash on hand. It seems like it retains most of its value used, so if you ever werent digging it you wouldnt be out much if you sold or swapped it out. If you are happy with the Freeze though, I wouldn't worry too much about upgrading.

As to the actual features, the Plus can trail off for like 20 seconds or infinity (as opposed to like the 4 seconds on the Freeze), it has an effects loop to mess with the trails, and the wet pedal is a fun tool. Practically speaking, the Freeze was a bit more difficult to use, I was constantly having to release at awkward times to get it to trail off the way I wanted. The Plus just does everything real naturally and easy. And the build quality is solid.

I'll just add, as to the sound quality, it was like the Freeze felt more synthy and no matter what instrument you play through it, the same sound note comes out of the pedal. The Plus seems to be less artificial and replicates your guitar tone exactly.