Some points to consider:
1. Sure hosting your blog within a bloging community can help in its initial development and promotion, but you lose ultimate control of the blog using a service like Google Blogger. At anytime for any reason they can shut down your blog. No thanks. This is a key point to understand I would never recommend or work on a client blog unless I hard full control over the code like I would have with WP or Moveable Type.
Also you can use Blogger fine and host it under your own domains. You don't need to use one of their subdomains. Wasn't sure if that as clear from the above explanations.
2. I think hosting you blog internally within your website has some benefits and hosting the complete blog somewhere else also has benefits. If the blog is being developed for a corporate website, I would suggest having it the actual website as a subdirectory. This creates some legitimacy to the blog. If the blog is slightly off topic or can take on a life of it own as separate community then maybe hosting it somewhere else is a better idea. I would not look at the
SEO benefits of the two choices because either way you will win, if you build and promote a great blog. I would look at what is best for yourself/client/visitors.
3. Interlinking or promoting your products on another website (whether it is a blog of not) is not spam. If your doing it and it makes sense to your end visitors then it is OK. If you set up a review website about all your products that you happen to be selling on another website you own, I wouldn't consider this spam. Of course I would rather have that great review content on my main website other than another.
4. Don't make decisions based on how you would figure the search engines compute IBL's. This IBL stuff is still such a big mystery and even if you did put some facts together who is to say it doesnt chnage all together the next day? The fact is, if you build your website with your end users in mind the links will come naturally. With this being said I would never consider building out a separate blog to increase IBL's to my main website.
In my case I put my
SEO blog on my
www.jaankanellis.com domain name because I didn't have anything there yet and I though it would be a good idea to add something. I hardly ever use it to link to my
www.kbkmarketing.com website.
Just to recap:
Blog because you want to or having something to say, not for
SEO reasons. The
SEO benefits are simply a side effect/by product of giving back to your community/business niche with your professional knowledge..