These overhead pedestrian pridges - or Ubergangssteg - are a distinctive feature of European prewar tinplate, and once you get the bug, it's hard to pass them up. I have 21 at last count... Marklin, Bing, Fandor, HWN, Hornby, Beckh, and a few American and some unknowns I haven't identified yet. It seems that not a lot of people collect them, so if they interest you it's a good time to be collecting.
Some of them can get pretty ornate. The one that you say you just missed on eBay (Marklin #2060, c. 1910) is nice because of the double stair flights with landings; some of them are just single long straight stairs. This one was also unusual because of it's length - 23", enough to bridge 2 or even 3 Standard Gauge tracks.
Generally, they were built for either Gauge 1 or O Gauge. The thing to look for is the height clearance under the bridge. Especially some of the Modern Era Standard Gauge is a lot taller than either prewar Standard Gauge or the Gauge 1 tinplate these bridges were made for. The O Gauge walkways tend to range from 4" to 6" height clearance; the Gauge 1 walkways can range from 7-1/2 to 9-1/2". This long Marklin bridge has 8-1/4" clearance, but that's from the table top to the underside of the walkway, you loose some of course with the height of the rails on the track itself. So it can work for Standard Gauge, but is a little low to safely run everything under it.
I have made sub-bases for some of my walkways, especially the Bings which tend to be a little lower than the Marklins, to raise them up about 1/2 to 3/4 inch - just use a block of wood a little larger than the tinplate base and cut steps into one end, paint it gray or other color to blend in on the layout. That way even some of the tall McCoy Standard gauge locomotives can go under.
They are a lot of fun and seem to be endless variations. They look good with some figures on them watching the trains pass underneath.
The page that Fred posted a link to, is a great help in identifying them. Just back up a couple of pages from his link, to the Ubergangssteg category page (not just Marklin), and you can branch from there to all the walkways made by all the manufacturers.
david