Depends how much you like blue lights and the Beach Boys, I guess!

Best bet is, go play one. Take your current arranger, set it up next to it, play through the same speakers... Does the T4 make you go 'I GOTTA have this!'?

Then leave, come back a week later without your current arranger. Play the T4 again. STILL feel that way? If so, it might be time to change. If not, save your money for the T5. Should be out in about 18 months, at this rate!