lol Yup, similar story here. I got the XB700 one day last year because I'd never heard a real bass-cannon-type headphone before, and I ended up loving it. Then I got a good deal on an XB1000 one day, loved that even more. And then I figured getting an XB300 and XB500 just to complete the set wasn't going to cost a lot, so I just went for it for the giggles.
In terms of value, the XB1000 is hard to figure at the moment. The cheapest one on eBay at the moment is $600, and there are a couple closer to and even over $1,000. But those are just asking prices. Doesn't mean they're going to sell for that. I bought mine last year for $300, but the headband is flaky and the pads were done for. One in good shape like yours appear to be can probably get you more like $350 or a little more if you're not in a rush.
XB700 seems to be good for about $100-$150, I think I paid $120 for mine. XB500 looks to be worth about $70-$100, I paid $50 for mine. Yours in good condition could probably get you up to the higher end of those ranges.
The NIB XB300, no idea what that might be worth. I bought mine with bad pads for $30, but it looks like nice ones can bring over $50. But yours being NIB, those can cost as much as any collector is willing to pay. Just depends on how long you want to wait to find the collector that wants them badly enough. There's a couple NIB XB300s on eBay at the moment for $150-$300, but again, just because that's the asking price doesn't mean that's what they might sell for.