Is the 2013 13" rMBP your only computer? Do you travel frequently? If the latter you might want to consider a 12" MacBook, which is feather-light and very small and would satisfy the urge for something shiny and new.... However, yes, it's only got the one USB-C port and so could require also purchasing some adapters/dongles, etc., especially if you need to connect to peripherals which use USB-A (USB-3) ports.
Ah, but that brings me to another suggestion. So you want something new and shiny, eh? How are you fixed for backup solutions (i.e., external drives)? You DO faithfully back up your machine(s), right? Well, here's an idea for something which fits the bill of something new and shiny: Samsung's T5, an external SSD drive which comes in four capacities (256 GB, 512 GB, 1 TB, 2 TB). Plug one of these babies into your 13" rMBP and back her up very, very quickly -- the device is really tiny and really fast. Inexpensive? Well, no....external drives with a "platter" or "spinner" drive in them are going to be significantly less money, but, hey, the big thing going for the T5 is its speed, its sleek appearance and small size as well as, yeah, that major cool factor.......
The T5 has just been released, so its predecessors, the T1 and the T3 may now be available for a little less money. Really, though, if just starting out with external SSDs, the T5 is the way to go. Such a difference from "platter" or "spinner" drives!
These aren't available at the Apple Store, but can be purchased at Microcenter (a brick-and-mortar computer-electronics store in various locations around the US) and of course online through Microcenter's website as well as on Amazon and at Samsung's own site. Someone also told me that Best Buy also has them in retail stores and online, but I haven't checked that out.
Before anyone asks, no, I'm not a sales rep for Samsung, but I am totally in love with Samsung's series of external SSDs and have been using them since the T1 first emerged on the market. As time has gone on and my budget has permitted I've gradually been shifting to making these the core of my supplementary and backup drives system.
Itching to spend a little money on some electronics? If you decide to hang on your current 13" rMBP a while longer, maybe it's time to give her the gift of speedy backup.....