It's hard to determine really what people are going to pay as it depends on what is available (for example, i am trying to buy a cheap shuffle but none seem to be left from the TD offer). I think you are on the right track with ebay. Find out what each sells for on average on ebay, and then package it up (or offer to sell in pieces).
Personally, I would put it all in one offer but sell individually.
Also, my personal rant, is about need. Why are you selling this stuff (what do you need)? If you want to just get rid of it, sell low. If you want to buy a nano/30gb, sell for just that price. If you want lots of $$$, then sell high. People always ask me to sell stuff on ebay for them. When I tell them they will get probably 1/3 of what they paid for it, many change their mind (not always the case, but always be ready for bad case scenarios). Obviously, they don't want to sell that bad.
Anyway, my two cents. Personally, I wouldn't give too much for a used mini. I've been seeing new ones going for $180-$200 here and on craigslist. PSP I can't comment on. Iskin, should be packaged with the mini, same with the headphones (unless they are different). A dock would be nice as an extra (if they want to pay).
Hope that helps
Education is when you read the fine print. Experience is what you get if you don't.
--- Pete Seeger