in general, things tend to evolve (in a better way) and that's why we have winxp with its eyecandy and other gismos here and there, or osx...
I noticed that companies begun to understand that beauty sels (can't disagre with that
so they improve among other things, the interface (we have a good example on SI>XSI , LW4>LW5.5>LW7 etc)
Of course this changes of look (and sometimes placement of known function in the new ui ) made some waves, but the general idea is that it worth the effort to adjust to a new ui.
in maya's case alias instead having a dep. for ui design, preffered a diffrent aproach.. let the user design his own ui the way he sees fit.
So , although the ui remains much the same, the added new controls ant others functions related JUST FOR UI ITSELF.
It is amazing how many new things they implement to help the user to build the ui he wants...I know because i begun to make my ui since maya4.
A bad example is Photoshop whom only starting v8 you can change the default shortcuts and assign new ines (still the best 2d app in the market thow)
And to answer your questions:
you bet it improved my workflow,(you always do things when you relly need them, right?) and even if it took me some time to leatn mel it worth a lot the effort and time, not mentioning the ui but learning a lot of stuff about maya along the way.
This is not final , I always add things along the way.
It is not like drag-n-drop shelf icon, but the mel is structured verry logical an it takes me few sec. to ad a button or a group of new commands as soon as i discover that i begin tu use them more and moore.
what you see on the left is actually the old toolbox cleaned up of all its functions (never need them anyway) and ad my own buttons and menus.
When you click on one of the items in the list above it , the menus and buttons change to that speciffic type of work (like the shelf more or less).
There are only mel scrips( no plugins or dlls) most og them are maya's originals with some mods and relocate them to a new folder so i have both maya riginals and mine (mine loads first 
So wherever i go i thake the disk with my settings and put them in the new pc and voila... copy paste, and ready to work...
they are user specific and they can be deleted along with my user, without harming the pc.
Or if i want i just rename the maya folder and i'm back to its oiginal ui.
Or ,by pushing a shortcut i can switch to one big viewport the size of my entire screen.
I tried to make it as flexible as i need it.
Oh, the UI is mine 100% but the scrips and commands are part maya's, part downloaded (others scripts... thaks all)
and part a combination of those two.
I will release it maybe (not necesarely that someone finds it usable, but maybe for its coding and internal structure, or somethind usable there) after i will make it even flexible... I'm still unsatisfied with some things, the most important one is to be able to mod it without going to a script editor...just an ui settings window.
i'l post an animated gif to see ti working....