What attracts me to 3000 is that I will be getting 220dpi out of my 12MP files with it, vs 180 with 3880
where are you coming up with those numbers? a 12 mp file is @3k x 4k pixels in dimension. If you print that to an 8x10 print, you will be at 400dpi. If you print it at 16x20, you'll be at 200dpi. it's the size of the image vs. the output size that determines this. (internally the printers are working at 360/720 dpi ... both the same so it's a lot more complicated than that. Maybe you're seeing that 180 is the nozzle density in the head, (but that's the same for both printers), so that's how many drops it can spit out at a time, but that's why the printer can't print a 1" wide strip on each pass. If printing at max resolution (which vertically is 1440) the printer will pass over each inch 8 times.
So the question is whether the smaller dots, which you probably only get by forcing the 3000 to its highest resolution of 5670x1440 (using the smaller dots at the other resolutions probably won't get enough ink on the paper) would result in a real world visual difference, and I concur with Phil, I've seen both (and sell both models) and unless you use a loupe you won't be able to tell which print came from which printer (and even then probably only if you know what you are looking for and have a high powered loupe).
Several good points I've seen mentioned (from my perspective both as an experienced user and a dealer). Build quality .. the 3880 is a workhorse, solid and designed for serious use. It rarely clogs .. probably the best printer epson has ever made and maybe the best printer anyone has ever made (imho). The 3000 is a good printer but not in the same category. The difference in ink costs is substantial, but as ernst mentioned, if you don't print a lot that's not helpful. You can use the ink cartridges far longer than epson recommends without any issues, removing them and gently agitating them as Jeremy mentioned. I recommend turning the cartridge upside down before oscillating it gently and then setting it down that way for a few minutes.. You can do 3 or 4 at a time, just hold them together as a group. Do not shake. Something to do every 6 to 8 weeks ... don't need to do it a lot.
Finally, the 3000 is a 13" wide printer, the 3880 is a 17" wide printer ... personally this alone sways most of those I sell too, unless they just don't have the budget and really don't print a lot. Ok by me because most of them are bringing in stuff for me to print on my 3880 within a month or two.
(i guess the 3000 does do something the 3880 doesn't do .. DVD/CD's, if you need that. That's the only reason I have one setup in my store).