So I've done some thinking about this, and I actually think I'm going to buy three floor burners plus leg extensions instead of a Top Tier. There were really only two reasons I was considering a Top Tier: consolidating everything into one stand, and being able to run everything off one propane tank. Is that really worth $500 to me? The extra hassle of this lifting/rolling problem probably negates it.
I considered only buying two burners, which is what I have now, but I can't tell you how many times I've wished I had a third. When I brew, I'm always doing extra projects in addition to the main batch. Sometimes I'm making tomato sauce, sometimes I'm pressure canning veggies (or wort!). And sometimes I do partigyle batches.
And finally, I'm sure some people will suggest I instead get a much cheaper bayou cooker or similar, but I want 1) Blichmann's wind shielding, and 2) I'm ready to have a quality piece of equipment in my brewery. I used to be excited about the DIY aspect of homebrewing, but now I just care about the brewing. I'm actually less interested in a brewstand now and more excited about the fact that I can get out each burner as needed.