Little difference, if any, on Matte Black-compatible papers.
No difference in the black D-Max of matte that's true but there will be improvement with deep colors in the oranges, reds, magenta and purples...
Look, it may be hard to pass a discount if money is really tight (although the 2880 might be a more realistic option) but at this point I would seriously suggest you DON'T buy almost 3 year old technology...sure, you'll be able to get ink for a while but the moment the 3880 ships, that will be the only printer that will be receiving longer term support and software updates.
Note, since the 3880 won't be shipping till Oct, the odds are there may need to be a 3800 driver update (I don't know this, but I'm thinking due to Snow Leopard it may) but after that the 3880 will be "current" and the 3800 will be "former" technology.
Seriously, I would buy the 3800 for $300 less...maybe 1/2 price, but if you can wait, you should. The color gamut is larger and the resolution output is worth it.