Just get the goddamn rMBP 2.3/256/8! It offers way better value than anything on the market including the current classic MBP. Try configuring other laptops with the same specs as the rMBP. Also your mistake is thinking that the ultimate RMBP has increased longevity over the base rMBP. Well this has not been the case ever since intel switch over to their tick-tock system.You're absolutely right that money is a lot of my thinking here.
When I ordered, I spent just over £3,000 on this machine with the intention that it would be my main computer until early 2016 really.
I have serious doubts that it will last that long right now. Not that the hardware will break or anything, just that I will feel the need to upgrade this machine far sooner than 2016, and as such I should probably be buying a cheaper laptop now and actually planning to upgrade in 18 months or so?
Its better to go for the base rMBP, keep the $1200 in cash and have shorter upgrade cycles for say 3 years. When the time is there sell the rMBP and use it with the $1100 in cash to buy a new one. That is value. Either way the ultimate rMBP is still going to perform similarly as the base rMBP in 2016. Nothing is going to change that. It is your thinking that is flawed.
So just stop whining. Jesus christ. You already have been given advice in this thread