So many Spectrums were made that they aren't worth that much - maybe with 150 games you might get up to £100-£150 but the keyboard membrane will almost certainly be shot and a fair chance it won't work without being repaired if it has been in a loft.
Yep - the original Spectrum didn't have a joystick port so you needed an adapter - and there were 3 varieties making in a nightmare for programmers
As for the ZX81 - my first computer and my first game was Football Manager. I have videos I did for a film that will sadly never see the light of...