yeah, the wah would definetely be a good investment. but beyond that id try some synths like suggested above. like the digitech bass synth wah or the ehx bass micro synth if funds allow. a flanger would be cool, but the only time it really has the potential to stand out would be during a bass solo. also, the ehx q-tron or micro q-tron would be cool. its kind of an auto-way pedal with adjustable parameters. and a fuzz would probably work better than a distortion in most cases for a rather chillin, trippy sound. id reccomend the mxr el grande fuzz pedal for that. heres the webpage, with a demo
http://www.jimdunlop.com/index.php?p...p_and_e_detail
lastly, you might also try either an eq or a di pedal. mainly for tone shaping. or even a di/compressor like the aphex bass xciter to prevent possible volume spiking, like when swithing on/off the pedals. even though pedal volume controls can remedy this, its nearly impossible to get volume adjustments dead on, and a compressor would likely help this