as others have said, you are unlikely to be stopped but two other considerations from me:

- crew will sort of know who is in their cabin and who's not (more so in Club than in Y) so you wandering about might raise a question or eye brow from one of them (unless you are wearing your F PJs and I personally would be too mortified doing that - though I know plenty of others do and enjoy it).

- your cabin is your cabin. so many will tell you that paying more allows you to do more / flying F means you are at the top of the hierarchy and everything else below is up for grabs, but I'd say the CW cabin is not designed to be the stretching area for F pax - nor the WT cabin actually. just like I wouldn't say it's ok for an F pax to raid the CW Kitchen (though I've had crew bringing stuff from there - but that's for them to decide whether it's appropriate or not. if you are hungry in F, you have ways of getting things and it's not officially the CW Kitchen). nothing majorly wrong with it but I find the whole "went for a walk in between drinking as much champagne as I can to see how poor people travel" a bit distasteful.

Happy Flying.