I'm in the exact same boat. My 2011 MBP is about at it's end, but Apple makes nothing that makes sense to buy right now. A very flawed and expensive MBP, and underpowered Air, and a impractically think MacBook.
I bought my machine with 4GB of RAM and a 500GB 5400RPM Drive. I now have 8GB and a 1 TB SSD. To ensure a new Mac will last, I would have to spend around $3k to future proof a MBP 15", and that's with the ticking time bomb of a keyboard.
I admit, I'm tempted to buy a used Mid 2012 MPB to get me buy the next year or two in the hopes that Apple can figure out who they are, and what their customers want.