I'm not that knowledgable on Nimbus's but I'm failry sure they are designed to be single engined boats, in any case at 32ft a single will always be more efficent than a twin.
I think if you find a twin engined version it will be to cater for the UK markets rather peculiar insistance on two engines.
Cue lots of stories on how peeps would have died if they had not have had twins.