Buying/Trading Member Databases

[The Equivocate]

I have been looking for some wrestling forums to buy out and redirect to my own, when it occured to me that instead of just redirecting, I could take their member database and merge it into my own. I'm sure people have done this many a-time.

But what if you wanted to buy or trade a member database with a site that will remain open? Let's say I owned ForumA.com and he owned ForumB.com, and we each have 2000 members. We trade databases with each other, which then ups our member count to 4000 each. We can then email these members notifying them of the change.

On the same page, I could just buy their db from them, and gain 2,000 members.

1) Have you ever done this?
a) If so, did it improve activity drastically?
b) Did the new members complain that they didn't want to be added to this new site?
2) Do you think it's ethical to use their database to then email these members to let them know they are now a part of this site?