I'm still not convinced that the T2-T3 change was anything more than a minor incremental upgrade. What did you get? A minor tweak to the NTT for guitar parts, a tiny handful of new SA sounds, a handful of other sounds and some sliders.
I just can't see anyone who might actually have to pay retail wanting to change a T3 into a T4, especially if Yamaha dealers drop NEW T3 prices to $2500 (that's going to depress used value of your T3!) and the price of the T4 remain where T3 was prior to the drop (if not go up - it will be interesting to see whether Yamaha, who have kept the MoXF at exactly the same price as the MoXS, decide to rape their arranger users by hiking the price despite the recession).
Every time we have a new Tyros come out, we get all excited at perhaps the possibility that capabilities and features from the Motif line will make it into the arranger line. But it never happens. So, I wouldn't be holding my breath for multitrack recording, or synth arpeggiators, or decent, punchy drums, or vast increases in effects architecture, or Flash RAM for samples, or DAW control from the arranger's panel controls, a 76 weighted, or anything earth shattering like that.
You'll get a few more sounds, a few more styles, maybe finally a better Songbook, some minor OS tweaks, and that's about IT...
Just like you did last time!
If that's worth trading in your T3 and taking a, what? $10000 - $1500 loss, best of luck. I didn't see a mass migration from T2 to T3, and, knowing Yamaha tend to keep doing what they do until they HAVE to change, I doubt I'll see a mass migration from T3 to T4. Possibly a T2 - T4 or T1 - T4 migration might make sense, but unless you work for a music store, I'm not sure going T3 - T4 is a good move.
I'd LOVE to be proved wrong, though! Just imagine if the T4 actually DID have all we wanted....
No, it doesn't seem fair to raise your hopes up like this