I'm not sure if your topic is intended to start another board war with Multiboxers vs. Singleboxers or if you are asking real questions.

Just in case you are legit...

I'll explain my situation first on why I multibox.
I'm married to a non-gaming wife (well ok... she's plays the Wii).
We have 2 young children. One is 3 years, and the other is 3 months.
I have VERY little time to play this game. I play at most 2 hours at night after the kids are asleep....assuming they go to sleep..
When I log into WoW, I don't want to sit looking for a group for 1-2 hours.
I also have had nothing but bad experiences with PUG's so I do not group with anyone other than guild members.

Now..for the "how can you spend so much money? what a waste! Loser" comments.
It's $75.00 us per month to play...for a month...
I can (and do) spend more money in 1 night at a bar drinking.
Taking my wife out to dinner and a movie is the same, if not more than that.

This is a simple form of entertainment for me and nothing else. I enjoy writing the macros and seeing just what I can accomplish with my group.
For me the answer to your question "soo, does multiboxing wow add to the gameplay?" is yes. It does add to my gameplay because it allows me to play the way I want.