What use is the (caravan) spare wheel/tyre?

Hi. This is my first post. We (Mr & Mrs – seniors) started caravanning 2010 (directly after doing the CC Club course).  We have 2010 Swift Charisma 560.  I have read much about caravan tyre safety. We had planned to purchase new tyres at March 2015 service.  On a car with a full size spare one might introduce the spare into the equation on a rotational basis.  However, would I be right in thinking this would be just nonsense on a caravan?  Firstly there is the age thing; how much safe life would there be in a five year old, albeit unused, tyre which has spent its life under the van held tight into a carrier.  Secondly, I have just read the thread about using the Alko under-van carrier with some dismay; thanking our lucky stars that we have never had to use the spare.  And thirdly, if spare is steel (likely) and other two are alloy then ….

Notwithstanding that our van has been annually serviced by a reputable dealer (the spare and carrier assumed to be checked/greased) I have come around to thinking that the spare should only serve as a spare for use in an emergency and nothing more.  And even then, recognising my own limitations, if it had to be used in anger I would need someone else to do it for me, even if that meant recovering the caravan (on a loader) to an appropriate dealer/garage.  And, I have Tyron bands fitted so only someone versed in their use could do this for me.

Am I thinking straight?  I should be grateful for views/advice from other members.