They can actually be worth quite a bit- although condition is always a factor and if the set is complete. IF the box is still sealed it's worth even more.
For reasons I won't get into- I had to sell a bunch of my old Harry Potter and Batman Legos years ago and even though they were opened and built- they were only on display, I had the box, the instructions, and the unused sticker sheet all in M/NM (Mint/Near Mint condition) and made almost 3-4 times what I paid for them originally. Had they still been sealed in a M/NM box- it would've doubled that price easily.
Legos are worth more than you think- Google Lego theft and you'll see that people were hijacking semis full of them to sell on the secondary market- almost like "Fast and Furious". There is actually a Black Market for Legos.
Actually, I think there were "Hello Kitty" Legos at one point- or it might have been "MegaBloks", kinda like Legos, but a little cheaper, but they got a lot of licenses that Lego didn't.
Update:
It looks like there may have even just been a Sanrio brand building block system like Legos.