I've had a similar dilemma. I have two blogs, both used to link to my site. One is entirely about my product, the other about my take on the day's newspapers and magazines (I produce personalised newspapers and magazines)
I have decided only today to add one blog - spoofnewspapers dot blogspot dot com - to my site and leave the other - personalisednewspapers dot blogspot dot com as it is.
I also have a news section on my website but i'm led to believe the more fresh content the better.
So, i'd suggest having two blogs - one seperate and one on the site, that way you have the best of both worlds.
Hope that helps.