At this point I prefer developing the core and features instead of developing the GUI.
I couldn't agree more. Actually I like OS client design. It's super clean and simple with 100% usability. Any custom design should be at least as good as OS design, otherwise it'll be just meaningless gradients and nice buttons.
I was surprised why I used my first Bitcoin wallet and found it looked like software I was using a few years ago on XP. But I think some people kind of like that. Sometimes a really polished 'cool' website and design can actually put people off. Number 1 priority people want functionality and simplicity. Examples include Reddit, Drudge Report and DGEX exchange. Good design has to have synergy with the client in the end.
Dgex is perfect example. First impression is - wtf, welcome back to 90s, but as soon as I started using it I loved it. Bter (especially new is making my eyes bleeding), Dgex is super cool.
Btc-e is fine also. No design for the sake of design, just functionality.
Qora client screenshots didn't impress me also, but when I installed it I loved it.