It appears that this defect is the norm for the 4 gig player. I have returned mine back to sandisk and they are supposed to be sending me a new unit. Upon various phone calls to sansa support (both from the sandisk line and the sansa shop line), I received mixed messages.
Some of the “level 2” techs believed that my unit was defective and that the brightness across all clip sizes should be the same due to the same internal hardware. Another tech I spoke to said that the clear coat on the screen “may” be causing the 4 gig model to be less bright than the 1 and 2 gig models. My gut is that as many users have shown the same problem, all of the 4 gig models will have the dimness problem (but we will see when they send me the new 4 gig model).
As is, the 4 gig model is usable indoors (although I would still like more brightness). Outside, regardless of light level, you will not be able to read the screen whatsoever. This was also a problem with the 1 and 2 gig models being somewhat difficult to read outside, but the 4 gig model is impossible to read outside except at night.
I wouldn’t recommend the 4 gig model until they fix this issue. You don’t think it will be a problem, but at some point you will want to switch songs or playlists outside and it won’t be possible. That being said, it is entirely possible someone will find an ingenius hack which will solve the problem (while voiding the warranty).
It appears less likely that sansa will release the 4 gig model in other colors soon (ie in the next few weeks) as there is a large time gap between when manufacturing lines are changed and when stores receive new products.
Somewhat of a bummer, but I would stick with the 2 gig model for now. I hope this helps.