Your seats are allocated by HQ, the check-in agent if approached right may be able to change them in the morning sometimes, not always gonna work tho'
So I take it that you know all the other stuff you will get with PG that makes it worth it like the upgraded meal, extra legroom, PG only movie, Pre boarding, Pre departure drinks, dedicated crew etc. One of the nice things about the PG service is that on your way back you get a quilt and neck cushioning pillow instead of the blanket and little pillow in economy. Great for sleeping
Definitely worth it in my opinion, enjoy your hols and your flight