One reason NiCad's are still used is that they last twice as long (no.charge/discharge cycles) and withstand minor abuse much better than NiMh's do. The only two advantages NiMh has over NiCad is they are a bit less mass for equivalent capacity (number of mah's) and less toxic if they wind up in a landfill.
As to reviving an old battery, whether it be NimH or NiCad, do a forming charge which is defined as charging for 16 hours at 0.1C. You do not have to discharge them before doing this either. The only reason for discharging either NiMh or NiCad is to check their capacity which should be done occasionally to make sure they are still providing an adequate amount of power. On yours, I'd recommend doing that to be sure they are still okay and then do it every 6 months or so to be sure they are not degrading.
On your 12 volt PB, if it is more than 2 years old, it is probably over the hill. On Pb or SLA batteries, the main thing is to never let them get discharged below 11.9 volts, never charge an SLA faster than 0.1C and use a proper charger, one that has limited current and voltage cutoff.
For some good info on how to care for your batteries, check out the following:
http://www.camlight.com/techinfo/techtips.html
http://www.whenshtf.com/showthread.php?t=2153
http://www.hangtimes.com/redsbatteryclinic.html
http://dansdata.com/gz011.htm
http://users.frii.com/dlc/battery.htm