So I got ahold of a nifty piece of software called OpenSim, which takes advantage of the open sourcing of Second Life's code in order to allow me to host my own sim, independent of the SL grid, on my own computer. I can then access said sim with my SL viewer (adding the appropriate set of commands after the ubiquitous "./secondlife", which I immediately worked into a desktop shortcut) and get down to business.
I had tried this initially with DGiG, but it seems that that particular project is more network-oriented (it set my computer up as a server for a sim, but then it could only be accessed by another computer linked to the server, and I'm a one-computer operation here, folks).
So in the end, with the private sim up and running, what did it get me? Well, for starters, I'm no longer plunking down ten Lindens per upload just to see if the lines match up on my latest set of t-shirts, or if the sculpty I spent hours sweating over in Blender looks in SL like something my cat spit up. I can hack out most of the nearly-infinite irritating details without having to adversely affect my bottom line, and save the upload charges for finished products.
I'm sure that I'm not the only one who's noticed that ten Lindens per upload tends to stack up quickly when working on a project. If you're in the Averlast Gym at any point, ask me or Karine about the speed bag. Once the red haze clears and we untangle our fingers from 'round your throat, we'll regale you with the tale of the many frustrating hours involved in getting such a seemingly simple item made.
I thought about using the capabilities of OpenSim for a side business, like, say, creating .RAW files for islands and selling them on SLX, but a little research showed that to do it well would turn into more of a full-time task than I really have the ability or patience for. Maybe it's something to file away for future reference.