Um… well, why not start here?
http://www.apple.com/uk/macbook-pro/specs-retina/
Thinking irrationally? It depends – can you bullet-point the actual advantages you'd gain by upgrading? (The Retina display certainly seems like one serious difference.)
I don't think that you're thinking irrationally at all. Unless you have the i7 upgraded model, then the performance of that machine is only going to increase your desire to replace or upgrade your machine. But then again the 2012 non-retina cMB with the dual i5 outperforms the MBa with the dual i7 configuration.
The main differences between the 2 MBP are actually minor (in my opinion) when purchased stock.
The cMBP non-retina weighs more, does not have a retina display, and does not have AC WiFi capability built in.
The rMBP does everything that the cMBP can do plus it has a better integrated CPU (which of course it requires for the retina display).
Now, what I love about the 13" cMBP is its potential depending on what you would like to do or are willing to do:
PCIe 2.0 and SATA 3 have the same data transfer speed limit so replacing the 5400 rpm spinning HDD in the cMBP would decrease weight and match the R/W speed of the rMBP. And using the superdrive bay (if you never see yourself using optical media) can be used to house a second SSD to make the cMBP actually R/W close to double the speed of the rMBP.
Due to the fact that the cMBP has usb 3.0, you could easily purchase a USB WiFi dongle and have AC WiFi (which your 2011 cannot do simply sue to the fact that your machine has usb 2.0).
The cMBP has actual RAM slots that you can install up to 16GB RAM and replace if the modules fail. with the rMBP if RAM fails, the you will have to replace the logic board.
With the cMBP you also get a full ethernet port (so no reliance on an adapter) and the firewire port as well.
Much like your current MBa, the cMBP does not have a retina display, but that is really the only "shortcoming" that the machine has in my opinion. Battery life can be increased (slightly) by the addition of a SSD and by increasing the amount of available RAM and make it last almost as long as or even longer than the MBa.
Essentially, until Apple moves to PCIe 3.0 on their lineup of laptops, I don't consider the retina display to be a big enough reason to pass up the opportunity to get a really solid machine that could easily last 8-10 years with the right upgrades.