From a bp organizer point of view:
bp organizers are able to fix a bp price becos we usually bring in the goods at wholesale price, but we mark up lesser in order to offer the product at cheaper price than what is selling in the retail stores. And this bp price is usually inclusive of the international shipping cost.
For spree organisers, they bring in the goods on normal retail price, hence spreeist will need to pay the international shipping cost just like when you buy direct from the oversea merchants. It is not fair to give up your order just because the international shipping is too expensive. The organisers is offering a service by collating all orders with the aim to help save shipping cost for everybody and order the product on your behalf. Spreeist can always ask the organizers for a shipping estimates. I'm sure those who organize sprees frequently are able to give you a rough idea, especially if the oraganizers alway spree from the same merchant sites.
If you feel that the shipping is too expensive to be true after the goods has arrived, you can always ask the organizers for the a copy of the shipping invoice and divide the amount by the number of spreeist. This way you will know if the organizers overcharged you on the shipping.
Re. capping of shipping cost. I don't think that is workable. You cannot expect the spree organizers to the absorb the extras when the organizers is already not earning from the sprees she organizes.
Re. spree organisers not profiting, this I will take with a pinch of salt. There are various ways to get around. Nowadays, merchants send out emails to their frequent buyers with special discounts not reflected on their retail websites. So the spree organizers earn by not giving back the full discount to the spreeist. The spree orgainsers could have special 20% discount code but only give back to spreeist 15% discount, she earns the 5%. Shipping: The spree orgainzers can have special discount too but does not share the full discount when she request for the 2nd payment for shipping charges.
I think it all boils down to doing your homework, joining one that is organized by a trusted organizer with good reputation and most importantly, whether you join bps or sprees, join with your eyes open. Shopping is meant to be enjoyed so ~ have fun