I guess I could be considered a network expert..
As you say, the switch should be completely invisible to the SMP; it shouldn't matter if the links are faster than the hardware.
My home network is pretty extensive. My SMP is connected to a NetGear GS108Tv2 switch (Switch 2).
That switch is uplinked to ANOTHER GS108Tv2 at the other end of my house (Switch 1).
*ALL* of my NAS devices (5 of them) are connected to yet another NetGear GS108Tv2 switch (Switch 3), which is uplinked to Switch 1.
So there are three Gig-E switches between my SMP and my NAS box (SW2 goes to SW1 goes to SW3); never had a problem streaming any high bit-rate content.
One thing these managed switches provide is visibility. I had a problem with slow performance on one of my NAS boxes when I first installed it. At that time, I had UNMANAGED switches. I suspected I had a cabling fault somewhere but with dozens of cables to look through, I didn't know where to start.
I looked at the error counters on the devices where I COULD look, and all of them reported clear connections. The WDs, of course, provide no way of knowing anything relevant.
So I just decided to upgrade the switches to managed switches, and immediately saw which of the connections were racking up errors left and right.
It took me about 3 minutes to narrow the problem to two bad factory-made cables, which I repaired, and the problems went away.
Visibility is key when looking at possible network issues; and the cheap-o unmanaged switches give no visibility at all.
So. yeah, the managed switch cost $30 more than the equivalent unmanaged switch, but it saved me at least that much money in time spent troubleshooting.
Plus, it gives me all kind of cool geeky reports as to where bandwidth is being used at the WDTV, like the attached.