In the old days of digital photography [about 4 or 5 years ago ]; we were told that we should always work on a PS image at the size it will be printed>>30 x 40" photo should be 30 x 40" x 300 dpi in PS= lots of MBs

Is this still the case now we are getting far better; and larger original images off the camera? Like 78 x 52" x 72 dpi

I export from LR into CS3 and the image can be up to 23 x 15" at 240 dpi. Does the image really need resizing in PS before reworking, or is it just as good to resize with exporting from LR to be printed as a 300 DPI jpeg?

Just a note; I usually use the midsize raw which is 53 x 35" x 72 dpi