I'm thinking of posting a few bass lines to common valses, but before I do, it seems wise to air a few thoughts about how bassists seem to approach valses. Maybe this post will be sufficient in some way so that I won't have to do the work of notating what usually are very uncomplicated bass parts!
First, bassists often just play one note per bar in a valse. If the chord stays the same, maybe they'll alternate roots with fifths. If the tonic chord changes, say to the iv (in minor), the bass often supplies the minor third of the tonic, putting the rhythm section in first inversion, which leads more strongly to the iv. So if there seems to be little "walking" movement in valses, some movement is suggested.
Second, the duration of the one note per bar appears to be crucial to the 'swing' of the valse. I've heard some bassists just sit on the note for the full three counts, and to me that just sounds dead as dirt. The note should be lifted, maybe just before the last eighth note of the bar, and there should definitely be some indication of dynamics in the line -- maybe crescendo as you arrive toward a chord change? You know what to do.
Third, there's a really interesting guitar-bass duet on Tchavolo Schmitt's "Miri Familia." The bassist plays a combination of arco and pizz (often in that order), and that opens up some space. A strong arco 'pulse' on beat one of each measure sounds very Eastern European, very traditional. In fact, some Hungarian folk musicians use a very short bow (maybe no more than a foot long) to produce this effect. They lean into the one and make it last for longer than what one would mechanically expect -- and it produces this weird feel for triplet rhythms that make you nod your head like a drunk peasant. It feels good. So maybe there are opportunities to consider the bass's role in valses more creatively.
Fourth, I haven't heard too many bassists take solos on valses. I'd like to hear some.