i think you are wrong, you are free to have your own opinion but i dont believe that to be the case.
firstly, and this disproves your entire point of view: if that was the case and bad backlinks devalued and put a dent in the ranking ability of the site, then i could get my competitors deindexed and have them NOT rank.
But what you're saying is not true. You can place another website in a bad link neighbourhood. However, it makes no difference as there is always another site to replace it.
as far as google has said, all we know is certain types of links are valued LESS and its very specific.
secondly i dont believe that google can discriminate between spammy and "unspammy" links, this is a label you have given. there are sites with high outbound links and low pr that provide a low amount of link juice, there is no such thing as some of the concepts you are talking about.
You're making too many assumptions. Mattcutts has spoken about these points in his blog and there's other sources. For example, read this blogpost
http://googlewebmastercentral.blogspot.com/2009/11/hard-facts-about-comment-spam.html
Google now suggests that you REMOVE blog spam form your link neighbourhood and then submit your site for reconsideration in Google's index. That's why the tool is there, if Google penalises you, it gives you the option to resubmit for reconsideration.
Matt Cutts has spoke in the past about the trust filter (AKA sandbox). Although i can't find the link anymore.
I think, the best thing you can do is some tests. Numerous times it's been said that Google takes your link neighbourhood into account when ranking your website and if you have a bad link neighbourhood you're not going tog et very far at all. Which is why you have 500 links and you're nowhere to be found.
Here's a quote form the blog
Q: I've cleaned it up, but will Google penalize me if the hacker linked to any bad neighborhoods?
A: We'll try not to. We're pretty good at making sure good sites don't get penalized by actions of hackers and spammers. To be safe, completely remove any links the hackers may have added.
Also
http://googlewebmastercentral.blogspot.com/2009/10/dealing-with-low-quality-backlinks.html
What all this means is if you saturate your website with bad neighborhood links then they will affect your ranking. If you link/backlink to good neighborhoods and make sure your site is obeying all other good ranking rules then it will diversify and decrease the negative effect it is having.
Also, it's not that Google can't discriminate, It's simple because Google is very intelligent but mindful of not wrongly penalizing a trustworthy site.
However, you're giving it reason to.
everything you are saying is just what you assume. you dont actually know. im doing what works for me and im ranking multiple websites for competitive keywords.
good luck to you..
also never ever submit your website for reconsideration, that is silly - why would you draw attention from a real person at google to your site? do you want to get deindexed unless you are completely white hat?
Our sites are completely whitehat, that's why the rank better than blackhat sites with much fewer links.
I suppose it annoys me the misconceptions that other marketers spur onto people. Claiming 40,000 links to get to you page 1. In reality it's a false statement, you can do it much easier with a lot less links and a lot less hard work. Also Google picks up more long tails with a good site.
Really, i wouldn't be typing all this if it wasn't true. I'm trying to help.