if you already have the keyboardist, you do not need synth for bass guitar, imo.
work with him, not against him, and you can do wonders with you playing clean bass and him playing synth lines... that's the best option imo (also the cheapest)...
of course, if the music needs a second synth player, you or your guitarist might want to upgrade your equipment... I would suggest getting and learning to play a keyboard, it's not that hard... you're way more limited with bass synth pedals than with not being good at playing a keyboard... and for the price of a good synth pedal, you can already get a good cheap keyboard synth (I got me a Novation Bass Station, which replaced my Korg G5).
another option is getting different (non "synth") pedals. this is the most expensive and time consuming (and fun!) concept, with the least guaranteed results (at least in short term). if you just want to add another dimension to your e-bass sound, start with an octave pedal... I'd suggest an OC-2 (easy to get, cheap, good sound). Another one is Chorus. Getting to the next level with fuzzes and filters will take a bit more time, research and experiment... finish with a phaser, delay and/or ring modulator
But remember, music comes first. If equipment doesn't serve music, it's useless. Discuss it with your band members what you, as a group, want to achieve, and work in that direction. Trying to be louder/synthier/whatever than your band members will not get you anywhere music-wise (or otherwise) and will just make it an expensive hobby... not that it's cheap without the "gear competition"