It's been my experience that palet's shipping costs scale up very quickly. When I've ordered two items from them, my EMS cost was around $32-36 (North America), and when I ordered 3 items it was around $47. I think that's because they have some sort of calculation by weight (which is how EMS is priced to begin with). So I'm not sure how much the items weigh, but I'm guessing that, in the end, Himeya will end up being cheaper simply due to their shipping cost calculations.
Basically, Himeya eats some of the shipping costs when you order a lot (but bump up the cost of each item thanks to some extremely unfair currency exchange). Palet, on the other hand, gives you cheaper/more reasonable prices on the individual items, but charge a bit extra on the shipping to make it worth their while. So if you're ordering a few items, Palet's cheaper, but if you're ordering many items, Himeya will probably end up working in your favour.
In some cases, it's actually cheaper to use an agent instead, especially if you can find all the items at a Japanese web store for a good rate. Typically they collect a percentage of the total but only have a single fee per order, and then they charge you the actual EMS shipping cost. So, in some cases, that may be cheapest of all, but I'm not sure how it would work for your order since you have a lot of doujin items.
Anyway, in the end, I've basically come to accept that there's no cheap way to collect stuff from Japan!
Hope that gives you some food for thought, but hopefully others will chime in with their opinions as well. (I am wondering, though, whether we should split it into its own thread, but I guess we'll leave it for now...)