Wouldn't that blow the hot air back down and keep it in the case?
If you're talking about heat rising, it doesn't make a difference. As long as you have a clear path for the air to travel, i.e. no "dead spots", it's fine.
My thinking is the top intake would be pulled directly through your CPU cooler, rather than all the way from the bottom. As it is now, it's not getting much air after the PSU and GPUs have had their fill. The fan at the top would be almost exclusively for the CPU, and the front intake would be pulled right through towards the PSU and GPUs.
Also, this would lessen the negative pressure inside the case and in turn, pull in less dust.