Will I see performance boost if I add memory with these Page-In/Page-Out statistics?
The increase speed you see when starting Photoshop immediately after previously starting and stopping it is coming from the hard disk cache which cannot be increased, and adding more system memory will not make much difference unless your allocated memory is sufficiently high to require significant paging out to make room for the new app.  As any paging will have taken place on the first load, it's unlikely to require more paging on the 2nd attempt unless you re-access the data that has been paged out so that is get's paged back in, which you do not allow time for in this scenario.  Your page in/out figures need to be better detailed to allow for proper consideration - how long is this sampled over etc?