I use my computer several hours a day, so spending a few hundred extra (as a one-time expense every several years) to get something nearly perfect is worth it to me. MacBooks have occasional annoyances, but they are thoughtful and refined designs overall, and OS X is a great operating system. When you consider the amount of hours you use your computer, the cost amortizes to a few cents an hour. Especially with no other pressing expenses, it's a worthwhile place to put money to me. Compared to an automobile or housing, it's simply not that much money for something that makes a significant difference in quality of life to a heavy computer user.
If you're buying a full-price high-end Apple notebook, it's good to do it at the beginning of their lifecycle, as Apple rarely cuts prices throughout the product lifecycle. Otherwise, buy a refurbished model; Apple refurbs are very good deals.
A downside of the Macbooks Retina & Air is that they are much harder to upgrade than older Macbooks. My 2009-model Macbook (bought refurb in 2010) runs just like a brand-new machine during day-to-day use because I've upgraded the memory a couple of times as memory has gotten cheaper through the years, as well as putting in an SSD. However, Apple products do have very good resale value, compared to any other consumer electronics-- it looks like the computer I spent $900 on 3 years ago is still worth $500 or so, according to eBay.
Another thrifty option that'd still keep you using nice Apple products would be to buy a refurbished Macbook Pro or Air, waiting a couple years until the Retina display trickles down, then reselling the Pro/Air for around 2/3 of the purchase price and buying the cheaper future Retina product.
If you use Windows and are fine with it, though, a Thinkpad is a better deal.
Another note: does your employer have a 401(k) match? You should max that out as a priority over paying down your student loans-- if there is a 50% match, that's a 50% ROI opposed as to paying 3% on your student loans. If there is a match, you should put every possible cent in income remaining this year into your 401(k) to max the match.