Yeah I suppose you're right.. but I"ve found that people are willing to pay more to secure an item now then wait it out in a auction style listing and if you have immediate payment required you don't have to play games with your bidders/buyers as they will already have paid.
The only reason I don't like BIN with IPR is that it can discourage discounts if a buyer is looking ot purchase multiple items from you but you can always quickly edit the auction and take IPR off and after they purchase the item send them a new invoice
I only use BIN (I have a store, but I think I am going to close it and go with the 100 free listings and add BIN to each...I just haven't done the math yet to see which is more cost effective.)
I have noticed that in the Video game category, I have much more problems than other categories, so I may require IPR on them.
As far as combining, I think I have only had 3 people in 3 years that wanted to combine shipping that weren't already set to combine in the listing.
IDK, I think I have to rework some stuff since ebay has changed so much. I am not sure I am getting the best value, even with the 20% top rated seller discount.