Missingno doesn't corrupt save files. It's often blamed for braking games in ways like that, and it's quite easy to understand why given Nintendo's own erroneous reports on its effects -- but Missingno itself is virtually harmless, and has very minimal effects on core gameplay. In fact it's hardly a glitch itself, the actual glitch is the method through which you are able to encounter it. The only thing it damages permanently is your save file's Hall of Fame data, so unless this is particularly valuable to you, Missingno is 100% safe. As Bulbapedia states:
The Hall of Fame is corrupted because of its proximity to a buffer used to store decompressed sprite data, which is too small to properly hold MissingNo.'s garbage sprite data.
In addition to the Hall of Fame problem, if you use Missingno in a battle, it will scramble some Pokemon sprites and other graphics. However, this effect is not permanent; accessing the summary screen of a normal Pokemon returns this to normal.
Merely encountering, not necessarily catching, will cause Missingno to corrupt your Hall of Fame data, so stay well clear of it if you don't want to lose your Hall of Fame. The item duplication glitch also occurs immediately upon encounter, but this doesn't matter to preserving the Hall of Fame since Missingno breaks it at the same time.
If you are at all curious as to what Missingno is and why it happens, read this article. Its author pulls their information directly from Red and Blue's source code, so you can be sure of its accuracy. Long story short though, you're safe to do what you like with the item duplication glitch if you're prepared to sacrifice your Hall of Fame.
(Side note, this assumes you're playing an English copy of Red or Blue. In different localisations and also Yellow version, Missingno's sprite data will sometimes overwork the game's memory and crash the system, which may or may not affect your save file.)
