Wendy,
I would agree with Dave, "horses for courses," sums it up very well.
It is, of course possible to catch a lot of different species with one or two rods, however, how much fun would it be playing a decent Roach on a Carp Rod with 10lb. line?
Over the years I have collected an enormous number of different rods for different species, venues and methods.
Okay, I'll own up to being a terrible "tackle tart" but there is something indefinable about having the right rod for the job at hand.
These days I use a 13' Carbotech Feeder and a 13' Carbotech Float Rod for Barbel fishing.
I have a pair of Bob James Avons for most of my Roach and Chub fishing, but usually use these for leger/light feeder wotk.
I have several stick float type rods from 13' to 20' for trotting on the Avon.
For Waggler fishing I have 3 Drennan Waggler Rods and a Drennan Long Range Match Rod - these from my match fishing days when to save time in a match I would regularly set-up 3 or 4 rods all the same.
For Tench fishing I have a Drennan Float Rod and a pair of Century Feeder Rods which are an absolute dream to use.
I also use Century rods (3) for Carp fishing, but they rarely see the light of day these days.
Somewhere in my tackle room I also have a pair of Nash Pursuit Horizons at 13' 3lb. t/c.
(note i have to tidy that room up before Ron comes to stay as he is sleeping in that room)
Although having admitted to being an incurable tackle tart, even I won't go into the number of poles and whips that I have bought and used over the years.
Come to think of it, I had better do a full inventory if for nothing else than to update my insurance :-o)