I bought a new 2015 model, although in my case the Touch Bar was the main reason -- I absolutely hated the new keyboard layout (lack of Esc, no physical function keys, arrow keys are now arranged in way where your fingers can't easily find the right keys without looking down).

Unfortunately, turns out they're no longer made with a discrete GPU -- they only have an Intel Iris integrated graphics chip now, no AMD Radeon. The discrete model was discontinued in 2016.

As a result, graphics performance is horrible. It's especially noticeably bad with the scaled Retina mode. I have to use the scaled mode on my external 4K display because otherwise the UI becomes so small the text is unreadable. That's when you realize that Apple's approach to resolution independence is pretty crappy. You'd think they could just run in 1:1 and just render text, buttons and so on a little larger, but that's not possible.

That is what my entire office did too, holding out hope the next generation has a reliable keyboard and no touch bar

I'm hit with the not support of mojave with my 2011 iMac, and all the options now are bad, and cost a LOT for me (specially because SSD upgrades cost so much).

The ironic bit is that old machines are almost as costly as new ones...