You are right,I forgot about the iMacs. It will probably be a little longer than two years before they go completely 'retina'. I will therefore refine my prediction to state that in two years there will not be single new PORTABLE computer product from Apple that will not come with a retina type display.
iMacs may not go pure retina until five years (or possibly slightly longer).
I wouldn't say in the next five years. I wouldn't be surprised if the next redesign of the iMac brings some sort of retina display. We don't know yet when the next redesign will be, but probably between 2015 and 2016. Prices of ultra-high resolution TVs are very high right now, but they are dropping steeply and they may reach reasonable levels within a couple of years (the World Cup is just around the corner, and manufacturers want to sell a lot of TVs by then). Such price drop in high-resolution TVs will make it feasible to put such a screen in an iMac in the future.
Perhaps the resolution is not 5120x2880. If Apple releases a 2304x1440 MacBook Air in 2014, as predicted, it will break the pattern of quadrupling resolutions of previous devices. If that happens with the Air, Apple could well do it with the iMac. So, Apple could release a 3840x2160 iMac and call it "retina".
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Absolutely not. Maybe the RAM upgrade is worth it (if its not user upgradeable) but the Processor upgrade is a nonissue if you plan to keep the Mac for five or more years. If you plan to do so (up to date-) performance is unimportant to you.
I have the high end 2009 MBP 13" and performance wise its equal to the low end from todays point of view.
Just take a look at the specs of the 13" rMBP:
low-end: 2.4 GHz Core i5, 4 GB RAM, 128 GB SSD, for US$ 1,299.00
medium-range: 2.4 GHz Core i5, 8 GB RAM, 256 GB SSD, for US$ 1,499.00
high-end: 2.6 GHz Core i5, 8 GB RAM, 512 GB SSD, for US$ 1,799.00
The difference between the two first Macs is the RAM and the storage space (they both have the very same processor). That would make some difference. The RAM upgrade is definitely worth it, considering the timeframe, and the SSD space is always welcome. If you keep the laptop for so long, you're likely to accumulate a lot of files and may need this space.
As for the high-end, it may not be necessary. But, as Apple does not offer the possibility to upgrade the lower-end models to get 512 GB SSD, then you should opt for it in case you need more storage. It's US$ 300 for a slightly better processor (which may not even make a big difference, but it's marginally faster, which is not a bad thing) and 256 GB more SSD space.
You may, of course, opt for a custom Mac with 16 GB instead of 8 GB.
In any case, if you are on a budget, as it is apparently the case, I would go with the mid-range model, with a 2.4 GHz processor, 8 GB RAM and a 256 GB SSD. It's US$ 1,499, but it's more worth it than the low-end model for US$ 1,299.
If you are not, then consider the mid or the higher-end version with 16 GB, and, in this case, you would fork US$ 1,699 to US$ 1,999.
But if you really, really, like to spend some money to get the best overall in order to keep it for 5 years, then you could go with a maxed-out rMBP, and pay US$ 2,699 for it. Not worth it, though. I would prefer to buy a more modest machine now, and buy another one in a couple of years instead of keeping it for 5 years.