Robzula, I really like Speed Racer as well, and never understood why it was criticised so harshly. However, this topic is in the LEGO section, so from here on in I'm going to stick to that.
I think when we look at both the Speed Racer and the Prince of Persia lines, we need to look beyond the movies, the licenses, and the hype to the sets themselves. When you look at the Speed Racer line and how it did, you notice that the two smaller $20 sets did much better than the two more expensive ones. This exactly echos my purchasing, as I purchased the two smaller sets myself. When you look at these sets, each contained two really cool looking cars as well as some excellent looking figs. Both sets had around 200 parts giving them a nice parts/price ratio. Overall, they were very nice sets with good parts and good playability. Even if you cared nothing for the movie, the show, or the license, you could still appreciate the value these sets contained.
However, if you look at the larger sets which didn't sell as well, it's easy to tell why. The one set came with the exact same car contained in one of the smaller sets as well as a semi-truck. I'm sure most people realized that they would rather pay for the smaller set and get the same car as well as another of similar size that they could "race" together" rather than some random semi-truck with some strange stuff in the back that didn't make sense. I can't tell you how many times I saw this set sitting alone on shelves while all the others around it were sold out.
The other set was fairly nice (and I did consider buying it), but on thing really prevented me from doing so: the random "pit stop" and "finish line" elements that were included. They really didn't add much to the set other than increasing it's price. Also, the cars were nice, but didn't really mesh with the other racers, so there wasn't much of an incentive to "complete the collection." Overall, this set was better than the semi-truck one, but still had it's problems.
Now, as for the PoP, I predict these sets will sink or swim based on the merits of the individual sets as well as opposed to the success or lack thereof of the movie. Here's some thoughts on each set after a cursory glance at their LEGO pages:
7569 Desert Attack ($10.99)
So basically, this is a battlepack-priced set with quite a few figs including the PoP himself as well as two bad guys and a skeleton. However, what immediately stood out to me was the black horse. Has LEGO made a horse in black before? If they have, it's been a while. Also, I'm pretty sure we have seen that bush piece in dark tan before. Overall, this set intrigues me with all it's minifig goodness as well as that black horse and bush. Will other LEGO enthusiests see it the same way? Time will tell.
7570 Ostrich Race ($19.99)
OK, so it's pretty obvious that this set is basically the Hoth Base of 2010. The main selling point of this set is the new ostrich molds, which look pretty nice. The question I have to ask is, was there really as big of demand for ridable ostriches as there was for a ridable Taun-Taun? As cool as those ostriches are, I just don't see myself really needing to get them. However, I'm sure there are people are there who will. I think in the future, there may be a market for this set for those few completists/parts monkeys who missed out on their one chance to get their hands on some hot ostrich action, but other than that, I have to wonder.
7571 The Fight for the Dagger ($29.99)
My first thought when looking at this set was "$30 for a camel?" I should admit, though, that I've never been a fan of these small-scene sets like this. However, upon further inspection, I will admit that the minifgs and accessories are nice and there are some nice tan, brown, and gold pieces here. Also, I really DO want to get one of those camels, and this is the cheapest set in which it appears. I think this set's reception will be pretty mediocre, but could possible surprise me and become a hit due to the camel.
7572 Quest Against Time ($49.99)
I'm gonna be honest with you: I really see this guy stinking up the shelves with it's boring-bley self. I was initially excited when I saw that trans-yellow stuff and thought it was those old-school quarter-windscreen things that haven't been seen in ages. However, when I zoomed in to find that it was actually just a bunch of 1x2 bricks, all that excitment left me in a hurry. To me, this just seems like a really boring scene with figs that can be purchased in cheaper sets. Also, does anybody really need more of those sawblades? And by "more," I really mean "any at all." I can see getting this as a parts pack when it inevitably hits the 50% off bin, but until then, I'll pass.
7573 Battle of Alamut ($79.99)
Wow, what an improvement over that last set. I'm loving the wide variety of colors, minifigs, and playability. I can definately see this having some cross-appeal with Castle fans (especially the fact that they'll be able to get many of those castle parts in non-grey colors). With a great parts/price ratio, lots of minifigs, that new camel piece and plenty of other stuff, I can definately see this set doing well.
Anyways, that's just my take on these sets. I predict that most the sets will do fairly well, although probably not as well as the Indiana Jones sets that they're replacing. I'm sure they'll find their market regardless of how the movie does, and don't think that the fate of the sets is necessarily tied to that of the movie, despite what happened with Speed Racer.
And upon review I realize that this is a pretty epic wall of text: enjoy!