I used many of the basic scenarios but with twists to make them unique, and usually harder.
"....usually harder" is key I think. SS&SS is a brilliant game and IMHO the best at doing what it was designed for, it's only shortcoming appears with a lucky run of player die rolls making the scenarios no challenge for even very low level parties.
There is frustration about bad luck making a difficult scenario too difficult, but we find that serves to make you want to run the scenario again to beat it.
A scenario where a few lucky die rolls make it too easy is actually disappointing and tedious. There is no desire to re-run a too easy scenario to try and lose it.
Better to err on the side of too difficult than too easy.