Perhaps try the trial version to see if your computer has sufficient power to do what you want and the features you desire. I've never seen PD9, my old man has PD 10, i started with PD 11. I only downloaded 12 recently so yet to complete a project to comment much on processing speed. I5 is a dual core processor if I recall, rather than quad core of I7, so you may not get significant improvements over PD9 with their latest development.
The main two new features of 12, multicam and theme design is what made me upgrade. Multicam is awesome if you ever use two (to 4) devices, and theme design is good for short clips, say memorable day trips. I'm likely to use theme designer for a short clip to show at my wedding next year.
Hope this helps.