I am wondering if it is beneficial to submit to DIGG and other sites like that every blog post or is this excessive?
Yes, it would probably be some wasted effort submitting every one. It may also get you flagged as a spammer on sites like StumbleUpon (depending on the regularity of submissions.)
The best is that you submit it once nobody is submitting your posts for you. If the category in these social bookmarking sites is relevant to yours, just submit them. Submitting your links to social bookmarking sites is not just only about getting traffic, it is also about getting link juice and have a better search engine ranking positions. To know more about this, there is a video here by Stomper Net that will explains everything on this to you.
digg in general doesn't favour bloggers who submit their own stuff. I would suggest using other platforms like bloggingzoom.com, stumbleupon or mixx.com. changemod.com
Are there any people on DP that specialize in submitting to social bookmarking sites? If so please contact me with pricing and examples of other clients and how you have been effective for them. Thanks!
I don't recommend submitting every post to digg specifically. Although, you should try and add friends that are in your niche on StumbleUpon because you will see hundreds of targeted visitors from them.