One perk that an old Ratchet game unlocks in the forthcoming Ratchet sequel is useful. The other perk, is not.
Insomniac Games has kept to the Ratchet series' tradition by making the newest installment on the PlayStation 3 aware of players' activity in the older ones. Having played — and reviewed — the new Ratchet & Clank Future: A Crack In Time using a final retail copy, I was able to see how my save files for the last two games, 2007's Ratchet & Clank Future: Tools of Destruction and 2008's Ratchet & Clank: Quest For Booty, affect the new game.
I had completed both previous PS3 Ratchets and had the following perks activated automatically when I started the new game:
-My Tools of Destruction save file classified me as a returning customer when I visited A Crack In Time's weapons-vending kiosks. I was given a discount. Thanks to the lower prices and my collection of new bolt money throughout the new game, I found myself lacking money to buy the next available item in the game only once.
-My Quest For Booty save unlocked the pirate hat you see my Ratchet avatar wearing atop this post. The avatar appear in the game's community section, which displays a variety of player accomplishments and stats, shows leaderboards for many of those accomplishments. Players can customize their Ratchet avatar or look up the records and avatars of their friends. The avatar is essentially a visual shorthand for some of the things you've accomplished. For example, the pistol that Ratchet is holding in that shot looks as it does in the game, where I attached mods and selected its paint job.
Those are the unlocks I found so far that relate to the earlier Ratchet games, confirmed by a Sony representative. If I find any more I'll let you know.