I am an ex-Thinkpad 560X/Z user and avid Docking Station user myself
This particular model appears limited because of its ultraportable nature
However, are you aware of the Port Replicator with advanced Etherjet (p/n 05K4872)?
I have used it myself and was pretty satisfied with it, although not nearly as complete as the 2631 -
However, it features the following ports :
1 x Ethernet RJ-45 10/100-Base-T
2 x PCMCIA Type-III
1 x Floppy connector
1 x VGA out (15-pin)
1 x Parallel out (25-pin)
1 x serial out (9-pin)
1 x Game/Midi out (15-pin)
1 x Audio in
1 x Audio out
2 x PS/2 (mouse and keyboard)
1 x USB
A couple of years back, I used the PCMCIA ports to extend the PCI bus to a Mobility Electronics Easidock 5000, where I could add more PCI card, hard and optical drives... the works.
I had not to suffer because of the underequipment (by default) of my Thinkpad 560X and Z
Good thing was this port replicator was also useable with the Thinkpad 570 and its media slice, which I also used it with.
Fact is, I have every single docking station IBM put out (even the elusive and not very useful 3550), so feel free if you have any question
Hope this helps,