Just got a 2nd hand unicomp... not sure if worn out or it's just normal?

[bluejeans]

Space bar is very wobbly (kind of like on some rubber domes) and takes much less force to actuate than the other keys.  Actual keys are a bit disappointing, they feel a bit like not as stiff alps whites.  Also, the keycaps seem slightly glittery/sparkly.

[rowdy]

The first thing to check is the spring under the space bar - make sure it is not stretched, bent or something.

Also check the space bar stabiliser wire is properly in place.

The keycaps will probably clean up quite well, depending on what is on them.  Are they 1 piece or 2 piece?  1 piece are trivial to remove and clean, 2 piece only slightly more so.  Soaking in warm water with a couple of denture tabs usually works for me.