Matt Cutts with Google has publicly stated (as has John Muir here) that 404 and 410 errors are treated the same and won't hurt you algorithmically. But there is clear evidence that it can impact usability and customer experience.
In your case, the 410 permanently gone error code is the appropriate status to be returning in your situation. The pages aren't returning, ever. My experience shows that Google tends to drop 410 pages from the index almost immediately, whereas it can still take days or weeks for 404s to completely fall out of the index.
However, usability in your case comes into play. 30 days seems a pretty DRASTIC cutoff date for content (except in the case of finite classified ads, event listings, etc.). You may want to eliminate one hard-and-fast rule and look at this issue from a more flexible viewpoint. Can some of these 410's be redirected to more appropriate (read current) resources via 301s? How about link equity? Are some of these redirects actually worth salvaging and redirecting to more related long-term resources via 301s to salvage link equity?
Finally, bounce rate, time-on-site, and general usability continue to become more important from an algorithmic standpoint. One of the things I do internally with my sites and those of my clients is track the 410/404 error traffic on specific URLs and make sure that if these pages are still being searched for and/or visited that I am mindful of the site experience. First impressions do matter...especially on 404/410 pages.
I hope that helps. Good luck!
