[quote name='Romeo']You make it sound so easy!
Here's why I wonder this... Retro City Rampage is a cross buy game and shows up on my trophy list as one game. Yes I can be bought separately but if you own both it's one list, and it has cross save too. That's why I assumed every cross buy game was like this.[/QUOTE]
I don't know much about the cross-save feature, because I only have the Vita version, but I do know that All Stars is by far the most easiest platinum I've ever got. I got 50% of the trophies within the first week of playing the game, and I wasn't even trying for them. I am by no means a trophy hunter, I have about 10 platinums (bought the ps3 on launch and have been playing ever since, so 10 in that time isn't really that much compared to others), give or take a few, I only try for platinums on games I really love, but getting all the trophies in all stars was the easiest and least time consuming platinums I've ever got.
And when the PS3 version of all stars reaches $20, I'll buy it and go for the platinum on that version. So if you're concerned about acquiring trophies on both versions, don't be, because I guarantee you it's far easier and quicker to get both All Stars plats than it is to get a single plat in most other games. You don't even have to beat the campaign on the hardest mode (3 modes, normal, medium, hard), you just have to beat it on medium one time.
Then there's a bunch of trophies for performing a level 3 super with an amount of characters on their respective stages (lvl3 super with big daddy on columbia level, lvl3 super with ratchet on metropolis, etc, and several other charcters), and ALL of those trophies can be done in practice mode, with an idle enemy that just stands there and doesn't fight back. You can make it go by even quicker by just pressing start and setting your super level to 3, so you can do it instantly without having to build it up.
If the trophies are what's holding you back, then stop worrying about it and buy the game now, you'll get double the trophies for a miniscule amount of time and work.