Yea the 4 has those l-line and h-line plus the input #5 in the middle which can't do much but it's handy.
I never used the midi features even once so I can't tell you how good they were....

With the 4.0 they took out those extra inputs as well as the MIDI and a few other things such as the low eq cut switches, the mono button.. but then, in the 4.0 they added separate input meters on each channel, and the monitor outputs are XLR instead of RCA.. which as a sound guy I really prefer because they are harder to break than the TRS on most mixers.. and less adapters to deal with.

So yea, whether you like the cleaner layout, more rugged finish, better metering and connectors of the 4.0 or the greater features of the 4.. is a matter of taste. Having had both.. they sound the same as far as I could tell (I didn't do a side by side comparison) and I would happily mix on either one.

But these days, getting a great condition 4 will be tough as they have been discontinued pushing 10 years ago?? Not sure.. but a while! And now I see on the Ecler site that the 4.0 has been discontinued, they are only making the 2.0 still.. or, they now call it the "20". Which, I had a 2 (my friend now has it) and it was great, if 2 channels is enough.

Long story short, if you want to have the Ecler 4.0 experience, might want to pick one up while you can still get one in good condition.