I'm in the exact same situation. I have a late 2008 17" HiDef Core 2 Duo machine fully loaded out, but I haven't used it much in the last few years. With the iPad Air and the Retina iPad Mini, I just haven't had the need to lug the "big" computer around. In fact, the iPads were so good that I didn't bring a laptop at all when traveling anymore. BL: the key was portability and battery life. The iPads were better than my old laptop on both accounts.
Today, laptops are much lighter, smaller and have outstanding battery life. I bought the 13" Macbook Air 1.7/4GB/128GB HD a few days ago and loved it. It was light, very thin and had great battery life. My first full charge gave me over 12 hours of usage before it shut off. I did a mix of netflix, iTunes movie streaming, but mostly email and internet surfing. The speed was great, the laptop was completely silent (no fan running), although during my initial configuration installing Yosemite and other software, it became a little warm...nothing to worry about. 99% of the time the laptop was cool to the touch. The only concern was the screen resolution and color accuracy. I have the new iPhone 6 and that screen is amazing. The Macbook Air screen is good but not amazing.
So today, I went to the Apple Store last night and played with the 13" Macbook Pro with Retina display. That screen is amazing! Differences: $300 more, 4GB more RAM, 2.6GHz vs 1.7GHz processor, .5 lbs heavier, and slightly thicker at the front of the laptop. I purchased the Pro a few minutes ago and downloading Yosemite as I right this (I'm typing on the Air). I plan to use both for a few days, but I am already thinking I will be returning the Air, just by looking at the Pro screen as Yosemite is installing. BTW: the Air is slightly longer and wider than the Pro. If the battery on the Pro is anywhere close to the 9-10 hour range and the cooling fan doesn't kick on when doing normal web surfing, email, etc, there will be no question which one is going back.
Either way, you can't lose with either laptop. In my opinion, the screen, extra RAM and awesome, accurate retina display outweighs the slight increase in weight, slight decrease in battery life and $300 price difference.