Hi Pip,
I only ever use a 4 string in our band, we're a type of Prog Rock, Rock, Fusion, band thing
We do some instrumental stuff, I don't tap or slap ever, I don't reckon those techniques are a must in a Prog/Instrumental band, great if you use them but doesn't matter if you don't
What I do find helpful is getting into odd time sigs, being able to count often helps in that situation especially if you're playing a unison riff with an evil time sig, so I would try counting odd things. I find when I crack an odd count the riff or complicated line comes a little easier.
Our situation is similar to Sibobs but with one guitar, we too learn, write and jam together.
A link or two if you fancy it:
[url="http://www.myspace.com/multistoreyearthworm"]http://www.myspace.com/multistoreyearthworm[/url]
[url="http://www.myspace.com/monkeylump"]http://www.myspace.com/monkeylump[/url]