You won't see any improvement on the R3000 compared to the R3880. The minimum droplet size is not the deciding factor in output quality. The Epson's use variable droplet technology so depending on your print mode it will use different droplet sizes (or combinations).
Both will produce excellent results.
Makes me wonder then why Epson desktop models use 2 picoliter droplets as a minimum droplet size and other desktop models go as low as 1.5 picoliter. The variable droplet size exists for all models, some have 3 droplet sizes, some 5. The 3880 has a minimum droplet size of 3.5 picoliter. My line of thought has been that the wider formats have larger droplets to keep enough speed at the sizes they print and the larger droplet will be less visible on those sizes considering the viewing distance. The distance between nozzle and substrate can be increased with larger droplets as they will keep their course better so media that can not be kept flat over wider areas, like in wide format printers, will benefit. All compromises in view of the sizes printed. The definition/addressing (shape/placing) of the dot laid down with a pro head could be better and compensate the droplet size difference somewhat but that is all. The custom quad ink developers take the droplet size into account, where they see 4 to 7 different ink grades as good for wide formats (3.5 picoliter), the desktop models can do with 2 to 4 grades.
On the economy of the R3000 versus 3880, much depends on what volume is printed in a year. Roughly 1.5 ML ink counting per square foot. The 3880's 720 ML ink translates to 480 square feet of print in best case. The R3000's 234 ML to 156 square feet. Not counting the length of the printers ink tubes that have to be filled (must be about 30% more to fill on the 3880) and not counting the gloss/matte black ink switch cycles on both. Price difference of $ 580 between the R3880 and R3000 buys you about
470 ML R3000 ink carts which should translate to 314 extra square feet printed. All BHphoto Jan 2012 prices. If you print less than 500 square feet in two years then the R3000 is the better choice, not counting other factors. If you print more than 500 square feet in one year take the 3880. Between those numbers it is harder to decide.
met vriendelijke groeten, Ernst
330+ paper white spectral plots:http://www.pigment-print.com/spectralplots/spectrumviz_1.htm