Nah, I don't think so. The only time it'd be an issue is if Nokia asked for the devices back in a couple of years. At which point, it'd be free money. But, 500EUR is enough that people won't just be 'losing' their devices as soon as they get them, and buying as many replacements as they can. And this is on top of the whole NDA/agreement not to sell it etc.

I do know that if it was cheaper, I might be interested in losing mine if it started to break instead of sending it in for warranty, so I'd have spare parts for next time. But I'd never ever sell it; I agreed to the damn agreement after all!

That being said, I'm not so sure why people want them - Near as I can tell, it'll be many months before it's 'usable': No file manager, no OC-able kernel, none of the important bits that make the N900 so valuable. So... why not just get a couple of(cheap) N900s, OC the ****** out of them, and simply know they won't last as long?
If you do a custom OC voltage profile you can probably get most N900s up to at least 1ghz; swap tweaks and such can solve the problem of memory, and EasyDebian can help with nonexistent apps.