Import numbering schemes

I'm considering revising my current numbering scheme for images shot after 1.1.2010. In the past I used a system of name_YYMMDD_####. I would batch images and assign the numbers for a whole day at a time using Lightroom's renaming function. The subfolders where I stored the images had a matching name and each held a day's images, frequently that required combining several ingests into one master image folder. That works well when I shoot a lot and ingest regularly.

It hasn't worked well in a couple of cases:
- my snap-shot camera where I may accumulate a month's worth of images (or more) before ingesting. The date-named files are quite different than the actual image dates or I wind up making extra folders with only a couple of images per folder.
- when I want to publish or deliver images part of the way through a day's shooting. (i.e. I may unload my Canon and want to publish some of the images right away, later when I unload my Leica then those images may be interspersed in time with the Canon's images but the file naming doesn't clearly reflect this.)
- because I'm expecting to combine ingests later in the day sometimes I forget to rename since it doesn't get done immediately when the images are added to Lightroom's catalog.
- when I shoot very different items during the day they wind up sharing the same folder on the hard drive.
- when shooting crosses the midnight hour then similar images need to be split between folders and the numbering restarts in the middle of a shoot.

Goals for a modified system:
- shortest possible unique image name (more room for appending derivative info).
- keep each card ingest together in a single folder forever.
- allow assigning unique names at the time of import into Lightroom.

I'm pondering using Lightroom's "Import #" token and I can't find much info about it's function from Adobe. Does it go on counting forever? Is there a way to reset the counter or set the starting point. What would happen when I migrate to a new version of Lightroom? I'm thinking about using a series prefix to help overcome some of these possible limitations. For example:
name_SNNN_### (the "S" would be an import series ID, NNN the import number from Lightroom, ### the image number restarting from each import) limitations. Using 3-digits for NNN and ### would give me aprox. 25,000 imports of up to 1,000 images before the system broke. 4- digits NNNN_#### nearly a quarter million imports. Using that system if necessary I could change the series prefix each time I migrated to a new cataloging program and almost certainly never run out of useable import numbers.

I'm sure someone has used a similar system and Peter will point out somethings I haven't considered that makes this system less useful than the name_YYMMDD_#### system.

Any comments/suggestions?

Thomas