I know it's frustrating that Nintendo seems to be updating the DS at least every other year, but I think this is a very positive step (assuming they don't pull a PSPgo and raise the price).
I'm almost 30 now and when most of you get there, you'll see you start losing some of your eyesight typically. You don't have to be 80 years old to enjoy a larger screen. I much enjoyed the PSPs screen which is why I can't believe they shrunk it for the go. I have 2 DS phat's and this may get me to upgrade. I was upset that the DSi came out because like VC and WiiWare on the Wii(at least for the longest time), DSi has crap support. Yes, DS has a great library but there is absolutely nothing out there that makes me think I need to spend $170 to have a DSi. They should have just made a DS 2 and been done with it so developers were forced to make games for it. Having said that it'll probably still take me at least 1 killer app and and a price point < $150 to jump on board but this at least has me excited about the DS again. A 4.2" screen is 96% bigger than my Phat screen. I think that is a worthy upgrade. It's 67% bigger than the current DSi model. What's also interesting is since the PSP uses a 16:9 ratio and the DSi uses a 4:3, that one screen on the DSi LL will be 7% bigger than the 4.3 inch PSP screen.