Arguable...if you need a replacement, obviously fitting one will improve its value - 'cos as a non-runner its value is pretty low....
Whether a reconditioned engine rather than a second-hand replacement will affect the value is another issue. If you get a re-con engine from a well-known supplier - maybe Ital-Autos - which offer a guarantee, it'll cost you £1200+ (ish)...a second-hand good condition engine will probably be £700 - that's what I sell them for - and its debatable which is the best option. If you are selling straight away, then selling with a guaranteed recon engine should help the value, and certainly make it easier to sell. If you are keeping the car....it sort of depends on "whether you feel lucky, punk?"
EDIT: Just noticed there are three threads on more-or-less the same subject....not generally regarded as good forum etiquette ;-)