Don't panic, yet.
The handle of the Pacific Salt is made out of FRN, and while being a very tough material, FRN will flex a little. I haven't seen any folder with FRN handles without liners, that didn't have a little bit of horizontal play. However, I have abused my Salts quite a bit, and have never had any issues whatsoever with the lockup of the knife. Also, blade play on my Salts has not gotten much worse, apart from my Salt I, but I _really_ abused that one so I won't blame Spyderco for it.
There are some options to tighten the riveted pivot, but I have yet to try it myself. I simply didn't find it worth the hassle actually. My Pacific has a tiny bit of play due to the FRN, but it's a tough workhorse.
If bladeplay does get worse, or if you find the amount of bladeplay unacceptable, contact Spyderco's customer support.