1) Do I need to jailbreak the un-jailbroken ones before I sell them to maximize what they'll sell for? How much could I realistically get for them if I don't bother jailbreaking them (and leave that for the buyer to do)?
Yes.
Go to ebay, type "Apple TV 2" in the search, click on "sold listings" to see what the items actually sold for. Here's a link that does that for you:
http://www.ebay.com/csc/i.html?_from=R40&_sacat=0&_nkw=apple+tv+2&LH_Complete=1&LH_Sold=1&rt=nc
You can draw your own conclusions from the data there, but a quick glance leads me to the following:
-non-jailbroken Apple TV 2's are going for as little as $130 and as much as $230, with the median probably somewhere around $200.
-jailbroken Apple TV 2's are going for between $200 and $320, with the median looking to be about $250.
Hence (again this is off-the-cuff), I'd estimate you should reasonably expect to make an extra ~$50-75 per unit if you jailbreak before selling. If that $50-$75 per unit is worth the time it takes you to jailbreak and install add-ons, then do it. If your time is worth more than that, then just sell them as is. Since your stated goal is maximizing profit, I'd recommend jailbreaking.
2) If I'll lose out significantly if I don't jailbreak them ahead of time...do I also need to pre-install a bunch of things like XBMC w/several add-ons or is jailbreaking enough?
If you truly want to maximize profit, install XBMC and some add-ons.
If you do the above search with "Apple TV 2 jailbroken" and look only at the sold listings, you can do your own comparison.
http://www.ebay.com/csc/i.html?_fro...tv+2+jailbroken&LH_Complete=1&LH_Sold=1&rt=nc
It looks to me that items advertised in the title as just being "jailbroken" typically sell for between $200 and ~$260. Whereas as items that include words in the title like "fully loaded", or "XBMC", "Navi-X", "Adult Content", etc. tend to go for between $250 and $320.
3) My jailbroken ATV2 is on an older OS version. Should I upgrade it to a new version and then re-jailbreak it? What's the process for that? Have I already missed my window of opportunity to do that (I believe Apple just released a new OS update that supposedly fixes some jailbreaking holes)?
I just upgraded my two Apple TV2's to firmware version 5.2 (the latest) last weekend (Feb 24). I also jailbroke them and installed XBMC on both with the Hulu, Amazon and Free Cable plugins. The step-by-step instructions for doing that are here:
https://forums.macrumors.com/threads/1305573/
If the instructions are followed carefully it shouldn't take you more than about 30-45 minutes per unit, start to finish.
As for the "window" of time at which you can do that, I think that window is a fairly long time (many months at least). When you jailbreak using SeasonPass, that program creates a custom firmware package. The latest SeasonPass makes a 5.2 firmware by default, then has iTunes install that firmware on your Apple TV. I think when iTunes does that, Apple has to "sign" it. So eventually yes you can't restore to a super-old firmware. But I think they are still signing 5.0.2, and the current version is 5.2. So there will probably be a while before 5.2 stops being "signed".
Also, if you want to install a firmware that is NOT the current (for example, if you want to have SeasonPass make 5.0.2 firmware instead of 5.2), that is potentially possible using SeasonPass. See here for more info on that:
http://www.appletvhacks.net/2012/02/24/how-to-downgrade-apple-tv-2-firmware-using-seas0npass/
4) It seems like the main market for these things are outside of the USA. Is that correct? Do I need to sell internationally on eBay to maximize the selling price? I'm worried about getting scammed. What precautions should I take?
I don't know how to analyze this properly for Apple TV's because I don't think I can just look at the location of the buyers on ebay items unless I'm the seller, and I've never sold an Apple TV 2.
But I can give you my anecdotal experience having sold three iPhones on ebay. (one iPhone 3G NOT jailbroken, one jailbroken/unlocked iphone 3G, and one unlocked iPhone 4). I live in Los Angeles. In one case, the winning bidder was in Eastern Europe, and after winning the auction they simply refused to pay, saying it was too expensive (They were the ones that bid. . .?!). So I submitted a complaint/note/whatever to eBay and they refunded my listing fees. I re-listed the phone and ended up selling to someone in Jakarta, Indonesia. That transaction went fine. The only hassle was I had to fill out some sort of customs form at the post office when shipping. The other two phones I sold domestically, though I marked that I was willing to sell internationally.
The iphone 3G I sold to Indonesia went for $230, it was NOT jailbroken. The iphone 3G I sold domestically went for $275, it WAS jailbroken/unlocked. I think the bigger part of the difference in price was due to the jailbroken status of the second one. That probably mattered more than the domestic/international issue. (The iPhone 4 I sold for $300 last September, domestically, was unlocked by AT&T, not jailbroken.)
So, the risks of selling internationally include (in my experience) the winning bidder flaking out on you and you having to complain to ebay to get your listing fees refunded. That just cost me time, no money. I suppose you get that risk no matter what the bidder's country, though I have heard anecdotes that certain countries are worse for that due to difficulty enforcing ebay rules there *shrug*. If you do sell internationally and it goes well, you might have the inconvenience of filling out an extra form or two when you ship. And of course higher shipping costs, but as long as you make the buyer pay for international shipping, it shouldn't matter to you.
My advice: If you are willing to go through some extra hassle/effort, list the items saying you ARE willing to ship internationally. Since the Apple TV 2 is so small/light, personally, I would advertise free shipping within the U.S., but buyer pays shipping internationally. (The free shipping within the U.S. helps to encourage people to bid and drive up the sale price, in my opinion.)