Get the best computer in your price range and you won't be disappointed.
Agree with everything except this bit. I've been buying computers for years, and getting the best just because burns a lot of money.
Just turn the machines over and get another one more often.
For most people, a $1100 MBA will get all or 90% of the performance of a $2000 MBP.
So instead of spending 2k today, spend ~1k, pocket the difference (or buy something else you want), and spend another 1k in 2 years time.
In 2015, sell the MBA off (will still be worth say $500) and buy another current spec one for $1000-1200.
If you did that, once replacing in 2015, you've spent:
$1100 - $500(?) + $1100 = $1700 for the MBAs
or
$2000+ for the MBP (more if you get applecare, which might be an idea for an expensive machine), which you're still commited to using for another year.
The 2015 MBA will also most likely be faster.