I didn't sound of on your first post because I felt like so much of a small-fry!
Turns out I'm not that bad. I usually do 5 gallon batches as I am pretty much the sole consumer of my product. I wouldn't know what to do with more beer! Well, I would, but I know I shouldn't!
I usually have somewhere between 4-6 different beers I'm drinking - I get bored too.
Time is a major issue for me as well. Between work, parenting, etc, etc, I am doing good to get a brew a month or so off. My goal is to produce enough for my own consumption. As long as I get that done, I'm happy. I also try to plan it out well. For example, I'm planning on doing an Oktoberfest next week that will be occupying my fridge for a while. Consequently, I tried to get all of my summer needs met beforehand.
As for 3 gallon batches, I would say the big pro of that is 1) as you said, space 2) more variety 3) an untested recipe or 4) something you don't want a lot of. For awhile, I did 3 gallon batches of untested recipes so that if they were bad, I wouldn't have 2 cases of crap! I got away from doing that, though, when my daughter was born. Now, brew days are precious, and you can make 5 gallons in the time it takes you to make 3! I will still do a 3 batch if it's something I just don't want 2+ cases of.
Bottom line - do what you do and don't worry about everybody else. That's what is so great about homebrewing - you can go your own way. I like the way the Norther Brewer blog said it best: http://northernbrewer.blogspot.com/2010/03/subsistence-brewing.html