1. LOYALTY: I still very much enjoy my Phantom 3 Professional.
2. TRUST: The P3P was my first quadcopter and as easy as it is to fly I was still quite nervous in the beginning and had no confidence but I learned to balance the flight controls as well as the camera and I learned to trust it. That said, the P4 does seem to make it easier but the learning curve is not there anymore, at-least if you're a P3 owner.
3. I'M NOT A ROOKIE ANYMORE: That said, the P4 is as excellent of a quadcopter for first timers as was the P3. I'm sure a lot of P3 pilots lost their birds after flying into trees or having insufficient RTH settings; The new obstacle avoidance system is awesome but I feel I'm a little more seasoned and I've learned to manage to avoid such risks and still get some awesome shots and video footage.
3. RELIABILITY: The P3P is a reliable bird and it was born out of the lessons learned from earlier Phantoms. I'm sure the P4 has learned a few of it's own lessons but for it's price tag I don't see myself benefiting any more than what the P3 offers.
4. SAME CAMERA: I don't see much of a camera upgrade to warrant the price. After all, this is first and foremost a flying camera. I would LOVE to see a bigger camera sensor and perhaps an improved depth of field on the next Phantom. Perhaps a little bit of zoom for all the privacy people out there too.
5. COST VS VALUE: If you own a P3P then you realize that there is still great value there. The 'real' upgrades that I wish I had from the P4 upgrade are the faster sport flying mode, dual IMU's and compasses for extended reliability and perhaps 'maybe' the longer battery life. Other than those features I can't warrant upgrading until maybe the Phantom 5. I'm thinking a better upgrade for most P3P users would probably be a better computer that can edit 4K like it was nothing!
Again..this is only my opinions folks!
2. TRUST: The P3P was my first quadcopter and as easy as it is to fly I was still quite nervous in the beginning and had no confidence but I learned to balance the flight controls as well as the camera and I learned to trust it. That said, the P4 does seem to make it easier but the learning curve is not there anymore, at-least if you're a P3 owner.
3. I'M NOT A ROOKIE ANYMORE: That said, the P4 is as excellent of a quadcopter for first timers as was the P3. I'm sure a lot of P3 pilots lost their birds after flying into trees or having insufficient RTH settings; The new obstacle avoidance system is awesome but I feel I'm a little more seasoned and I've learned to manage to avoid such risks and still get some awesome shots and video footage.
3. RELIABILITY: The P3P is a reliable bird and it was born out of the lessons learned from earlier Phantoms. I'm sure the P4 has learned a few of it's own lessons but for it's price tag I don't see myself benefiting any more than what the P3 offers.
4. SAME CAMERA: I don't see much of a camera upgrade to warrant the price. After all, this is first and foremost a flying camera. I would LOVE to see a bigger camera sensor and perhaps an improved depth of field on the next Phantom. Perhaps a little bit of zoom for all the privacy people out there too.

5. COST VS VALUE: If you own a P3P then you realize that there is still great value there. The 'real' upgrades that I wish I had from the P4 upgrade are the faster sport flying mode, dual IMU's and compasses for extended reliability and perhaps 'maybe' the longer battery life. Other than those features I can't warrant upgrading until maybe the Phantom 5. I'm thinking a better upgrade for most P3P users would probably be a better computer that can edit 4K like it was nothing!

Again..this is only my opinions folks!