Hi,
Here's one option to have your cake and eat it too
Make the scans as large as possible (a huge 16-bit raw archival version which you can store on dvd or whatever), then make a duplicate downsized proxy file for editing and keeping on your computer.
On the small file, use adjustment layers for tonal edits, then if needed, drag them onto the large one for a high-resolution file with the same tonal characteristics.
I downsize the proxy files so that at 50% magnification, the entire image fits on my screen. That way, there will be less display interpolation artifacts (less than 33.3% or 66.7% or etc.) when viewing the entire image, but can also zoom in to see more detail.
Also, the proxy files are downgraded to 8-bpc for further space saving
In addition to global tonal edits with adjustment layers, you can make lasso selections for dodging and burning (also with adjustment layers) - but if you want to drag them onto the large raw file, you need to (temporarily) resize the small one to the EXACT pixel dimensions of the raw file, otherwise the masks will not align properly.
Hope this helps. I like the fact that a raw, untouched file is available for re-edit if the mood (or the technology or my technique) changes
p