A lot of the bugs I'm seeing are because I mis-package something or because some asset I didn't realise I used is in my data folder, or something of the sort.

So what I'm going to try is to set up a parallel data folder for testing. The plan is as follows:

• Rename Data as Data_work
  
• Create empty Data_test
  
• Copy the Skyrim .bas files, Skyrim.esp and the update files into Data_test
  
• Rename Data_test as Data
  
• Install my mod into my new (and hopefully pristine) data folder
  
• Test it

When I'm done, I can swap the file names again. A pair of .bat files should take a lot of the pain out of that.

I'll report how I get on.

Meanwhile, has anyone tried this, or something similar? How did it work out if so? Any pitfalls to watch out for?

Well, I come from a different perspective...as a developer, I like to keep seperate dev and test environements. To do that with Skyrim, I keep two folders on my machine:
\SteamApps\common\Skyrim.DEV
\SteamApps\common\Skyrim.TEST

I drop the extensionn to use that environment (folder). So while I am deving, Skyrim.DEV is just Skyrim. When I'm ready to test, I rename the folders. It's very quick and easy and keeps everything completely seperate. (I actually maintain a clean image of each skyrim version on my network drive so I can always revert back if/when needed. This has proven VERY useful to test new Skyrim Beta Releases and when updates screw everything up. I highly recommend this approach if you have the drive space.)

Having the complete Skyrim folder seperate was the only way I could "test" the 1.6 beta, but still "dev" on 1.5. Just had to rename the folder.

When I'm ready to test my mod, I build the BSA file. I keep all my mod install images in their own folder, so I make the BSA from that install image. (I always make my own BSA images, I never rely on the CK to do it properly, as it didn't.)

I hope I make sense. The rename process takes just seconds and I always know which environment I'm working with by looking at the other directory names.

Same approach, just you go one better and take in the Skyrim folder itself.

I don't have the disc space to keep historical copies, but I can probably free enough space for two copies of the game.

That said ... the multi-data approach seems to be working ok. I missed a couple of folders out of the initial copy, but nothing that couldn't be fixed in less than a minute of checking local cache

Agreed, it's about the same thing. The main difference is that renaming the whole directory includes the binairies, which is good when testing includes something like SKSE or for testing the beta builds.

My comment "I come from a different perspective" was poorly phrased. I didn't mean compared to your approach, I meant it as compared to other people are I have talked to about this kind of directory setup. It's so simple though, I don't know why not to do it (other than drive space). I would imagine there aren't many people, even on this forum, who do this.

I keep two complete separate installations of Steam on my computer. One in Programs(x86) on my C drive - the default location, and another under my Saved Games library, which is on another library drive. I change between them by logging out and back into Steam from the appropriate copy of Steam.exe. Tha also allows me to have a version of Steam on mySSD that has only Skyrim and the CK and another version of Steam that has all of my games without filling up my SSD. The CK is much more enjoyable to work with running from my SSD.