My feelings exactly.I'm excited about the 4. Any help on a screen is a welcomed issue. Try a Nex5 on regular setting then go to Sunny setting.
Self explanatory. The IS, yes very nice to have. Sure you can use 1600 and 1.9 to secure an image in low light but now you have options to get a clean image if needed. 400 at 1.9 is way different or even go to 2.8 etc. I welcome the IS. Many people bought the Pen cameras for that very reason. I know, more important with legacy glass but it won't hurt the GRD4.
The GRD's are as good as it gets. It took 2 years to find and implement the few changes over the 3. If Ricoh deemed it necessary to do this, there's a good reason. Also, it's a testament to how good the 3 really is.
The new processing engine. Well, I'm confident it will exceed expectations. The GRD's are for serious shooters. They don't care about zoom lenses, evf's etc. They care about the responsiveness of a camera. Once set up, the GRD never intrudes, it's just ready to work the way you like.
The new 4, I'm sure will add to that experience.