From my perspective, I'm not too worried about whether I enjoy the game or not, as I know LEGO games are good, from experience (LEGO City Undercover in particular, is an underrated gem for the Wii U).
And I don't mind if I can't 100% the game because I don't have all of the characters. And from what I've seen and heard from people who play the game, Sonic pretty much breaks the game anyway, so you should be able to get most things with just him. At the very least, anything involving traversal isn't a problem for him, even if he doesn't have the "expected" skill. He also has the "Athletic" ability that Wildstyle has, so you can even replace her with Sonic for most sections that would require her (only thing you'll need her for is Master Builder stuff).
And I have enough IPs I'm interested. Sonic, Portal, Midway Arcade, LEGO City Undercover, Scooby Doo. And then my sister might want to get a few of the more Hollywood stuff like Harry Potter, Lord of the Rings, and the Simpsons anyway.
The problem just comes in the individual price of the Packs. Like it's kinda insane. While you do get a fair bit of content from a Level Pack, I still wouldn't say they're worth €40 unless you REALLY like that brand (in which case, Sonic is a lock for me). I mean, you could buy a brand new 3DS game for that price, nearly. While I kinda understand why it costs that much (it likely funds the development of the game worlds, not to mention getting the licenses for more characters), from a consumer's standpoint, it's a lot to swallow. Especially since the toys don't seem to have much interactivity within the game. While I know Dimensions does use it's portal toy for actual gameplay, which is cool, the characters themselves don't really seem to grow or progress much in terms of upgrades. So the toys are mostly just keys for unlocking characters, vehicles, and levels, and nothing more.
I won't worry about it too much now. I'll buy Sonic when he comes out. And maybe the game itself will be on sale for Christmas or something. If not, I'll still get it then.