Well, most basses have a low pass filter in them.
Although, taking this seriously, you have a lot of tonal variations at the touch of a couple knobs and switches, from a Ric (which has on-board signal routing) to a Fender Jaguar and others which have active/passive switching (which lets you go from clean to boost, or switch between EQ settings). It depends what you consider and effect, but in some way everyone has had experience with them.
There are a whole bunch of disadvantages to having on-board effects that would normally be in a stomp box -- namely that most people play multiple basses and want the same signal processing available for all of them. Obviously you also can't change the order of effects and it's really hard to tweak settings on the fly (guitar players have a big advantage here). Oh, and you might screw up and have a crappy sounding effect that you either have to rewire or just never use.
Anyway, you'll be able to do anything that Cave effects can (albeit with limited success). Clipping circuits are super easy (just need 2 diodes and a switch) and putting a couple of these in series will get you a decent fuzz tone.
If you're serious about putting something into the bass, then an OD or fuzz is kinda lame as you may as well just have a stomp. You should go powered and use a
mini delay or
feedback circuit.
about cave pedals and reading about lou reed's guitar with built-in effects and an old vox viola bass with built in effects wade me wonder...
