Sorry for the delay in replying. Paper choice is largely a matter of taste and sometimes a matter of apparently wider gamut. I like matte because it doesn't glare (reflections), which I find distracting. The worst part of matte is said to be tonal separation of the bottom quartile of the tone curve. A friend who has Imageprint with Phatte black ran a couple of my files suffering from this problem. He used the new Crane Museo Silver Rag he had for testing, and we found that it made a bit of difference to this problem but nothing that really hits you in the face. The paper by the way is lovely, and I understand there is better to come from another manufacturer. So, in a nutshell, as new papers hit the market we need to keep re-evaluating what we like best to use.
One nice thing about Epson Enhanced Matte is the cost - so if you mess-up it is quite painless. These other high-end papers really are pricy by comparison. If you do prefer non-matte finishes, the 4800 really does reduce gloss differential and bronzing (I've personally seen evidence of this with prints from both the 2400 and the 4800), but whether or not it is worthwhile to up-grade for this once you have a 4000 - which is a great machine - only you can be the judge by getting some side-by-side samples done under your supervision by someone near you who has a 4800.