The lights are on
The Sly Collection was a great idea because a lot of people either skipped that series entirely, or played one of the games and missed out on the others. The Jak Collection was necessary because, for whatever reason, Sony has let that series sort of fade away (despite efforts such as Jak X, Daxter and Jak & Daxter: The Lost Frontier). But Ratchet & Clank has never faded away from Sony; Insomniac has gotten 4 games out on PS3, and soon to be 5. Everything the PS2 games did, Ratchet & Clank Future do better, and they've gotta be cheaper than this collection is by now.
I will say this though. Ratchet & Clank has never returned to the competitive multiplayer in Ratchet 3. The 4-player co-op in Ratchet: All 4 One was great, and seems to be where platformers are headed in generally (look at the co-op modes in Donkey Kong Country Returns, New Super Mario Bros., Littlebigplanet, Epic Mickey 2, etc.). Co-op is great, but Ratchet's Competitive mode was awesome too, and surprisingly fully featured, with vehicles and everything. The biggest reason I could see to pick this collection up would be to revisit that stuff.
And of course, it's not like the games here are bad. Sly's got more style and a better design in general, and the Jak games are more ambitious and reinvented themselves with every entry, but Ratchet & Clank have always been solid. I just think you should play Sly Collection, Jak Collection and the Ratchet & Clank Future titles before picking this up.