Okay, some comments. First, I thought I'd give you a brief history of the collection system. The "horrible" UI you see now is the 4th generation.
The first attempt was a series of simple checkboxes, meaning you check it to "own" it, and uncheck it otherwise. It was simple enough, but didn't allow you to own "multiples" of items
The second attempt was this complicated "web app" thing that even I couldn't stand. It never made it onto the live site, as I tore it down and started over (Engledogg knows what I'm talking about).
The third attempt was an uglier, cruder, but functionally similar version of what we have now. It was the primary interface for about a year and a half.
The fourth attempt is what we have now. Reviews have been sparse--all I really have are helpful comments like "the UI is horrible". Really I thought it was quite elegant, but apparently the users disagree.
Anyway, your suggestion is to bring back the checkboxes, but for group operations. Yes, I get it, like they have in gmail.
I could see something like that being useful, but I don't think it would be a match for the current model. For instance, the collection rows are currently hosted by the product records, so selecting "all" would be sort of an awkward concept. Rather, I think it would be more appropriate for the "table view" you describe. You're actually the first person to suggest this, but I can see the appeal, and I'll keep it on my living feature request list. The more people ask for it, the more weight it'll get.
I suspect that mass deleting your collection is going to be a somewhat rare use case, so I can't give it a very high priority. If I were to implement the feature quickly, I think I'd rather do it somewhere where people are less likely to fool with it and accidentally nuke large chunks of their collection. I could see having a "Member Controls" page, where you could do maintenance things like flushing your collection, or searching eBay for all the parts you're missing, and so on.
Any other suggestions?