I recently downgrade (upgrade?) from CDJ-900 + DJM-700 to DDJ-T1. The cash that I got from selling them I use it to buy DDJ-T1 + Dell XPS 15 (Highend spec, Core i7, 8gb ram, fullhd display etc). T1 uses Traktor (not Serato as with S1). But you'll get the idea.
1) I never used CDs ever since I bought the CDJs. Been only using MP3 with external HDD via rekordbox. Traktor mainly uses MP3 but there's always the laptop dvd drive if you need to use cd.
2) CDJ + DJM are cumbersome for travelling (I don't have a flightcase and they are expensive). DDJ + laptop is super portable. Great for house parties.
3) After selling off my cdj and djm, i now have a DDJ and a supercool laptop which i can use for other purposes other than djing.
4) Traktor has abundance of effects. Potentially more with software updates.
5) Waveforms looks cooler on traktor than on cdj.
6) Traktor can be customised/configured to your likings.
7) Snap and quantize features works great (for newbies), proud professional DJs must stay away from this features.
It's heart breaking for me to migrate from cdj to ddj. I always thought that its cool to have CDJs at your home to impress your friends compare to having a controller and a laptop. But i got over it and i have no regrets since. Hope this'll give you some idea.