i just bought a "new" macbook pro 15 on monday and will have it tomorrow. After many months of research (was going to go with an iMac), i finally decided on the current 15" 2.5GHZ 512SSD and 2GB card. the machine has applecare until feb 2019 and has like 70 battery cycles. I paid $2000 shipped - no tax. I looked at apple.com, and with tax, the apple care and computer, it would have been close to $3000. To me, that is worth it. the computer will last me at least 5 years (as my iMac has).
even if i had the dough to upgrade every two years, i doubt i would. i am using it for photography. the new machine is at least twice as fast as my iMac, and i really don't have any issues with my iMac other than it is outdated - as far as USB and TB ports go. I can't utilize usb 3,0 on all my external drives, which is faster than my FW800 drives.
if you can wait, used machines will get cheaper by a bit. if you cannot wait, price out that machine on apple.com and see if the savings are worth it to you. Also check eBay. there are some great deals there - just have to be careful/