Apart from the extra room that a bigger desk would provide for gear and whatnot...the important thing is that it would also allow you to position your speakers with a little more spread. As it is...you'll end up with mostly in-your-face mono sound.
It's a problem that many home-rec setups have...because most people have just a computer, LCD screen, and little else on their desk...and the rest of their "gear" is all ITB plugs and such.
Even so, there's a benefit from spreading things out, and also pulling back a bit, away from the monitors...so yeah, a bigger desk would help with that.
I know this may come a surprise to many...but the recommended spread for near-field speakers by some studio designers is 5'-6' for proper stereo imaging.