The cheesiness factor of a M7 depends on many things, not the least of which is the style of music involved.
In general, if it's formed by a passing note in the melody or harmony, it's no big deal (and often I won't duplicate it in the guitar accompaniment, just let it happen in the voices or melodic instrument lines). I tend toward spareness in my guitar accompaniment anyway.
If it's an extra note stuffed into the chord (especially when voiced for fingerly convenience and not for sound, to make it worse) for the purposes of adding chunkiness to the chord, which is probably its most common purpose in jazz, especially latin-derived jazz, it sounds cheesy. The more so the more removed from its natural stylistic habitat.
Try playing "The Girl From Ipanema" without those M7 and 6+9 chords! But don't you dare put them into "Barbry Allen."
-Glenn