I'm with Randy, on the points he raises. Theatrical luminaires are also frequently Big and Heavy. The newer lighting instruments, which use 575w lamps and dichrioc reflectors usually, are unlikely candidates to be tossed; they are relatively new. They superceded an older straight tungsten technology that used 1000W lamps, that were always expensive.
The only theatrical luminare that I can see being useful in the average studio is a fresnel focusing area light.
Strand made huge numbers of a quite nice small 6" glass lens version, called a Pattern/Patent 123. It took a 500W (or 750W if you don't want the bulb to live long) lamp, and it was suited for smaller throws.
Take care with old theatrical luminaires; the older techology wiring insulation on the in some times 60 year old wire is very likely to crumble the first time it is flexed, and will need to be replaced. Burned sockets, where the spring steel material has been heated so many times to have lost thier spring is another common failing of old theatrical luminaires.
If anyone is looking for 6" elipsoidal zooms, that were made in USA by Times Square Lighting in the early 80's built of modern capules 1000W sources, well I am involved in a theatrical community theatre group looking to sell up to I think 14 of them at $80CAN each, FOB Toronto.