This gives me the flexibility to 'suspend' items that may lead to excess bandwidth charges.

Personally, I find that more annoying than having to register. There are some items that are never really available, because when you click on them, you constantly get a "sorry, over bandwidth" page. At least with registration required items, you can get them if really want them.

As for spam...I've never really noticed a problem with Poser sites. But I have a separate "public" e-mail address I usually use fpr suspect sites, just in case.