And then, once one has their expanded brewery, where does one brew? You'll be exiled out of the SWMBO's kitchen... 
Ah, but I *am* SWMBO...

I want to stay self-sufficient with my brewing (Ye Olde Alewife), so keeping things manageable is key. I don't weigh a lot more than 10 gallons of beer... though that is changing as time passes and my brewing improves :-) ... and frankly I'm a 50-something librarian with noodle arms, which has also dictated smaller batches and partial-mash.
Mashing in the kitchen in my 2- and 5-gallon coolers is easy enough (and makes the house smell great). But brewing all-grain half-batches, as I'm increasingly doing, requires split boils, and I'd also like to get out of the kitchen for some/all of these brews to both enjoy the outdoors and be able to hose down any mess afterwards. Plus I'd like to move up to 3.5 - 4 gallons (about the most I can handle). But as you point out, with scaling up, other dependencies start to emerge, such as chilling.
I bought the Bayou SP10 with an Xmas certificate (easier to cook on than our gas grill during an earthquake/power-outage, or that was my excuse anyway) and I'm shopping around with about $35 in Amazon/gift certificates to augment the kettle purchase. No hurry, I'm just shopping/musing. There's nothing fundamentally wrong with my current setup for now. I met another local "librewian" at a library conference and we've been planning a brew day, and seeing how she manages her setup will be useful.
My gut inclination is that I would not regret buying a 30-to-36-gallon aluminum kettle regardless of whatever I stepped up to later on for homebrewing. Whether it's homebrewing or holiday cooking, there comes a time in most of my cooking projects where every single large pot is occupied... one more couldn't hurt. I prefer stainless steel aesthetically but think that will have to take a back seat to other realities.