My argument for you losing the 360:
The PS3 does have some great exclusives that are definitely worth playing and it does have blu-ray. The online aspects are of course free and that will save you the equivalent of one game as opposed to buying a Live sub. Cross platform games don’t perform any less or any worse so you will not lose anything in that respect.
In most cases, moving from the 360 to PS3 will have you giving up some things to gain a lot more:
Lose the Live sub > Save money and still be online.
Lose regular DVD > Gain Blu-ray.
Lose minor exclusives > Have the chance to play some great ones.
My argument for you keeping the 360:
If you’re a huge fan of being online and enjoy the dashboard features of the 360, you should keep it and Live. Yeah, PSN is free and the online capabilities are mostly the same. However, the functionality and service of Live is, in my opinion, miles ahead of PSN. The 360’s features in terms of friends list and social aspects, as well as things like the store, make that sub worth it over free PSN.
I tend to find myself using Live to watch more HD movies than I do buying a blu-ray or getting anything from the PS Store. I think it would really come down to how much you enjoy the features of being online. I still think the 360 is better in terms of anything online.
What I really think:
If you have seen everything you think you will want to see then trade in. You can’t go that wrong either way. I would say though, try and borrow a friend’s PS3 if possible and try it out for a week. Get to use the dashboard and the machine. PSN is free so it’s not like you need to spend any money to experience the full features of the machine.
I personally cannot stand the PS3’s dashboard and inviting friends to games, checking trophies and messages is a pain in the arse. Not a huge one but it’s a small pain in the arse with the PS3 to no pain in the arse with the 360. I recently traded in my old Elite for a new 360S Kinect bundle and I love it. Not so much Kinect, that’s gathering dust, but the console itself is great. Plus, I just don’t think I could betray my 360 and play ME3 on the PS3.