I have the exact same iMac (mid-2011), and I agree with much of what the OP has said.
First of all, lets not compare apples and oranges. The 2011 base model should be compared to today's base models, not special i7 CTO-configurations - of course those will be quicker. Please remember, there were i7 configs and higher-capacity VRAM GPUs, even SSDs available in 2011 as well IIRC. The comparison doesn't serve a purpose here, in my opinion.
Comparing the base MBP of 2011 to the MBPs of today, the MacBook Pro has seen significant upgrades. The entire line now consists of Retina-screens and SSDs as standard. The MBP has received a new case, reduced bezels, et c.
Since 2011, when our iMacs were released, the iMac has become thinner, but only at the expense of the SuperDrive (which I actually use from time to time). Making the rMBP thinner made sense, the iMac - not so much. Other than that, it's only the incremental upgrades which have happened across all product lines, PC or Mac. It has received a bit faster Wi-Fi and approx. 20-25% higher performing processors. I think these are very modest improvements after 4 years. HOWEVER, the 21.5" iMac thinner design did not only come at the expense of the SuperDrive, but also reverting back to a 5400rpm 2.5" HDD, compared to the 7200rpm 3.5" HDD of the 2011. That will actually have much more of an effect in day to day use, compared to the processor change. That in a negative way. Oh and the 2011 DOES have an IPS panel, just like the models after it.
First of all, SSD should be standard in the iMac, just as it is in all other computers Apple offer, even if only available as a no-cost option for 256GB.
Secondly, the iMac needs a new design in my opinion. It has now looked the same since 2009, that's nearly 6 years. Making it thinner does not count as a new design.
You all seem very limited in terms of what Apple COULD do to the iMac, as if the iMac has now reached its limit. Here are only a few ideas, although maybe not to everyones liking:
* Improved ALL-IN-ONE functionality. Bring back Front Row, at least to the 27" model. Add a display input, allowing people to finally connect Playstations, Xbox et c.
* New design. (Remember the revolution from iMac G3 > iMac G4 > iMac G5? Those happened in 4-5 year periods)
* Backlit keyboards included w/ new iMacs
* Et.c.
I think there's lots that could be done to the iMac if one would only think outside the box. I think its evident that Apple is not selling as many desktops as they used to, and thus have chose to spend their R&D elsewhere, i.e iPhones, iPads and laptops. I can't help but thinking that now is an ungrateful time to buy an iMac. It's a great computer still, but add the SSD/Fusion Drive and you're looking at a lot of money.
Oh, and yes - the Retina iMac is the answer to many of the problems above, but it's even more expensive, way too expensive for someone not utilizing a 5K screen. Moreover, the computer is still a first gen product and I for one am not willing to deal with the UI lag and heat issues.
That said, I'm a bit interested in upgrading to the 27" model and I'm considering my options.
Either, just picking up a mid-2011 27" model and upgrading it with an SSD. It would make a faster computer in day-to-day use than the base 2013-model without SSD. I'd also get to keep the SuperDrive. These 2011 models can also be had very cheap, so that's a plus for me as a student.
However, I've also seen several deals for the 27" late 2013 base model, so while the above still holds, I could see myself getting the 2013 if the price was right, and if I'm able to install an SSD into it.
We'll see I guess.