Keep in mind that someone who buys one product gets access to all files uploaded to it, even in the future. That includes all files with special prices as long as the buyer has paid the minimum amount to access them. You might want to make each asset pack a separate project, and make regular bundles with reduced prices that bring all the asset packs together. That however could be a problem if you have a lot of them, since there's a soft limit of at most 20 projects you can have. So it depends. Hope this helps!