I fully agree with Marco. Yes, it’s an investment, but it’s just something that comes with the profession. You need to know what the future holds. Right now, Apple is the only one with a high-DPI laptop, but you can be damn sure it’s what we’ll all use in 5 years, no matter which platform you prefer.
I think right now the perfect setup is a Retina MacBook Pro, and a non-retina external monitor. That way you have both (like Marco said, type that looks great on non-retina can look bad on retina and vice versa).