I have it on Steam, and I'd say it's definitely worth it. I wanted to purchase this game since I had first seen it, but I didn't have money at that time. I waited.... and then Steam brought me a complete pack with 5 full games including Trials 2 Second Edition, for the same price of one game! I obviously purchased it . It's very fun.
While this looks interesting, and will seriously add replay value to the game, i highly doubt that it is even close to the possibilities of LBP. It's just a level editor (probably a good one). LBP is not just a level editor.