I didn't see any enhancement in P3D over FSX. As Ghandy said, the things are very much the same, with P3D adding some commercial features and benefits and another interface.
So my framerate and image impression wasn't changed at all and, after the trial month, I would have to spend at least 50 bucks for just another FSX. Not to mention the need for extra installers or the one on copying over FSX addons and hoping for a flawless operation.
Some devs offer separate installers and support, others will reject any support issue arising from running their soft in P3D. So be aware of the extra work needed and also keep in mind that some stuff may not be worth the time invested. For the tweak and fiddle folks, this may not be a downside though.

Maybe P3D 2.0 will change vital parts, really improving e. g. performance and some wonky FSX glitches and flaws, but as long as P3D is that close to the 2006 (2008) FSX, there may not be a good reason for a change. However, if that trial month is still available, maybe you folks can try and test. Even with the strongest faith, I couldn't see a difference here.

I'm ok with FSX. We both grew old together, so to speak.  ;D I've bought XPlane though as it really offers something new. Seems like a sim to watch for me. Not replacing anything on FSX (for me) yet, but looking really nice and offering a great support and feature set right out of the box.

Fun thing so far is that one is not familiar with the dev names there. So it would be nice to see CS at least doing some experimental release, just to check on the market value of XP releases. There are some established devs in that small XP market and they don't offer a real XP10 model yet, so you currently only see enhanced XP9 versions. However, e.g. that CRJ they are running there does look very nice.
So maybe CS sees it as a test bed of some sort when converting something like the 727 into XPlane.