yeah, it really depends. To suggest bass and drums are always necessary to make a clean bit interesting definitely isn't true, it just depends on the part. if you are just arpeggiating a couple of chords than it usaully is necessary
for example check out quo vadis' myspace, where they should have a rough mix of one of their new tunes, which starts with a single arpeggiated chord on guitar-but the fretless bass work and drums make it cool
however, more complex acoustic/ clean guitar work can sound fucking stunning with 0 accompaniment. usaully a lot more shifting of chord forms/roots and melodies between chords.
After this thread went up a wrote a simple clean piece that I think will be more helpful to explaining the advice I gave earlier about making clean bits less predictable/ more unique
hopefully, I'll be able to get it up next weekend-kinda busy with school
Also, it occurred to me to point out that its a mistake to feel obligated to include clean parts in your songs, especially if it feels really forced. No ones gonna say "fuck these guys" just because your band excludes clean guitar work
I'm not trying to discourage you from writing/working on clean stuff, I jut wouldn't include it until it feels natural is all.
Mostly, as others have said, just mess around-nothing good ever gets written intentionally!